refactor(isthmus): configure unquotedCasing via constructor, not setter

Drop setUnquotedCasing() in favour of constructor parameters, following
the same pattern as executionBehavior. This is the only approach that
is free from all three issues raised in review:

- No naming ambiguity (was withUnquotedCasing, then setUnquotedCasing)
- No subclass slicing (copy-return approach silently dropped DynamicConverterProvider overrides)
- No mutation window / no need to document call-ordering constraints

unquotedCasing is now a final field. Entry points:
- new ConverterProvider(Casing) — convenience 1-arg constructor
- new ConverterProvider(extensions, typeFactory, Casing) — for custom schemas
- existing 8-arg all-args constructor gains Casing as last parameter

All narrower constructors default to Casing.TO_UPPER as before.
IsthmusEntryPoint switches to new ConverterProvider(unquotedCasing).

Author: nielspardon

isthmus-cli/src/main/java/io/substrait/isthmus/cli/IsthmusEntryPoint.java

@@ -60,7 +60,7 @@ enum OutputFormat {
   private Casing unquotedCasing = Casing.TO_UPPER;
 
   private ConverterProvider converterProvider() {
-    return new ConverterProvider().withUnquotedCasing(unquotedCasing);
+    return new ConverterProvider(unquotedCasing);
   }
 
   /**

isthmus/src/main/java/io/substrait/isthmus/ConverterProvider.java

@@ -81,6 +81,21 @@ public ConverterProvider() {
     this(DefaultExtensionCatalog.DEFAULT_COLLECTION, SubstraitTypeSystem.TYPE_FACTORY);
   }
 
+  /**
+   * Creates a ConverterProvider with the specified unquoted identifier casing.
+   *
+   * <p>Uses {@link DefaultExtensionCatalog#DEFAULT_COLLECTION} and {@link
+   * SubstraitTypeSystem#TYPE_FACTORY}.
+   *
+   * @param unquotedCasing the casing to apply to unquoted SQL identifiers during parsing
+   */
+  public ConverterProvider(Casing unquotedCasing) {
+    this(
+        DefaultExtensionCatalog.DEFAULT_COLLECTION,
+        SubstraitTypeSystem.TYPE_FACTORY,
+        unquotedCasing);
+  }
+
   /**
    * Creates a ConverterProvider with the specified extension collection and default type factory.
    *
@@ -98,6 +113,21 @@ public ConverterProvider(SimpleExtension.ExtensionCollection extensions) {
    */
   public ConverterProvider(
       SimpleExtension.ExtensionCollection extensions, RelDataTypeFactory typeFactory) {
+    this(extensions, typeFactory, Casing.TO_UPPER);
+  }
+
+  /**
+   * Creates a ConverterProvider with the specified extension collection, type factory, and unquoted
+   * identifier casing.
+   *
+   * @param extensions the Substrait extension collection to use
+   * @param typeFactory the Calcite type factory to use
+   * @param unquotedCasing the casing to apply to unquoted SQL identifiers during parsing
+   */
+  public ConverterProvider(
+      SimpleExtension.ExtensionCollection extensions,
+      RelDataTypeFactory typeFactory,
+      Casing unquotedCasing) {
     this(
         typeFactory,
         extensions,
@@ -106,7 +136,7 @@ public ConverterProvider(
         new WindowFunctionConverter(extensions.windowFunctions(), typeFactory),
         TypeConverter.DEFAULT,
         createDefaultExecutionBehavior(),
-        Casing.TO_UPPER);
+        unquotedCasing);
   }
 
   /**
@@ -213,29 +243,6 @@ public Casing getUnquotedCasing() {
     return unquotedCasing;
   }
 
-  /**
-   * Returns a new {@code ConverterProvider} identical to this one except with the given unquoted
-   * identifier casing. Follows the same copy-returning convention as Calcite's own {@code
-   * SqlParser.Config.withUnquotedCasing(Casing)}.
-   *
-   * <p>The default is {@link Casing#TO_UPPER}. Use {@link Casing#UNCHANGED} to preserve the
-   * original casing of unquoted identifiers in SQL statements.
-   *
-   * @param unquotedCasing the casing to apply to unquoted identifiers
-   * @return a new {@code ConverterProvider} with the specified casing
-   */
-  public ConverterProvider withUnquotedCasing(Casing unquotedCasing) {
-    return new ConverterProvider(
-        typeFactory,
-        extensions,
-        scalarFunctionConverter,
-        aggregateFunctionConverter,
-        windowFunctionConverter,
-        typeConverter,
-        executionBehavior,
-        unquotedCasing);
-  }
-
   /**
    * {@link SqlParser.Config} is a Calcite class which controls SQL parsing behaviour like
    * identifier casing.

isthmus/src/test/java/io/substrait/isthmus/UnquotedCasingTest.java

@@ -1,6 +1,7 @@
 package io.substrait.isthmus;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
 
 import io.substrait.isthmus.sql.SubstraitCreateStatementParser;
 import io.substrait.plan.Plan;
@@ -11,9 +12,9 @@
 import org.junit.jupiter.api.Test;
 
 /**
- * Verifies that {@link ConverterProvider#withUnquotedCasing(Casing)} controls the unquoted
- * identifier casing consistently across both CREATE TABLE parsing and query parsing, so that the
- * table name stored in a Substrait {@link NamedScan} reflects the configured casing.
+ * Verifies that the {@link ConverterProvider} unquoted casing parameter controls identifier casing
+ * consistently across both CREATE TABLE parsing and query parsing, so that the table name stored in
+ * a Substrait {@link NamedScan} reflects the configured casing.
  */
 class UnquotedCasingTest {
 
@@ -27,27 +28,23 @@ void defaultCasingIsToUpper() {
   }
 
   @Test
-  void withUnquotedCasingUnchanged() {
-    ConverterProvider provider = new ConverterProvider().withUnquotedCasing(Casing.UNCHANGED);
+  void constructorCasingUnchanged() {
+    ConverterProvider provider = new ConverterProvider(Casing.UNCHANGED);
     assertEquals(Casing.UNCHANGED, provider.getSqlParserConfig().unquotedCasing());
     assertEquals(Casing.UNCHANGED, provider.getUnquotedCasing());
   }
 
   @Test
-  void withUnquotedCasingToLower() {
-    ConverterProvider provider = new ConverterProvider().withUnquotedCasing(Casing.TO_LOWER);
+  void constructorCasingToLower() {
+    ConverterProvider provider = new ConverterProvider(Casing.TO_LOWER);
     assertEquals(Casing.TO_LOWER, provider.getSqlParserConfig().unquotedCasing());
     assertEquals(Casing.TO_LOWER, provider.getUnquotedCasing());
   }
 
   @Test
-  void withUnquotedCasingReturnsCopy() {
-    ConverterProvider original = new ConverterProvider();
-    ConverterProvider copy = original.withUnquotedCasing(Casing.UNCHANGED);
-    // returns a distinct instance — original is not mutated
-    assert copy != original;
-    assertEquals(Casing.TO_UPPER, original.getUnquotedCasing());
-    assertEquals(Casing.UNCHANGED, copy.getUnquotedCasing());
+  void getUnquotedCasingReturnsSameInstance() {
+    ConverterProvider provider = new ConverterProvider(Casing.UNCHANGED);
+    assertSame(Casing.UNCHANGED, provider.getUnquotedCasing());
   }
 
   /**
@@ -74,7 +71,7 @@ void defaultCasingFoldsTableNameToUpper() throws Exception {
    */
   @Test
   void unchangedCasingPreservesTableName() throws Exception {
-    ConverterProvider provider = new ConverterProvider().withUnquotedCasing(Casing.UNCHANGED);
+    ConverterProvider provider = new ConverterProvider(Casing.UNCHANGED);
     Prepare.CatalogReader catalog =
         SubstraitCreateStatementParser.processCreateStatementsToCatalog(provider, CREATE_STATEMENT);