Propagate WITH clause to subsequent SELECTs in UNION queries

In ClickHouse's EXPLAIN AST output, the WITH clause from the first
SELECT in a UNION ALL/UNION query is propagated to subsequent SELECTs.
The inherited WITH clause is output at the END of children for those
subsequent SELECT queries.

This fix applies the same WITH clause propagation logic that was
already implemented for INTERSECT/EXCEPT queries to plain UNION queries.

Fixes tests:
- 01515_with_global_and_with_propagation (stmt5, stmt11)
- 03671_pk_in_subquery_context_expired (stmt7)
- 03611_uniqExact_bug (stmt2)
- 03033_analyzer_resolve_from_parent_scope (stmt4)
- 01236_graphite_mt (stmt4)

Author: claude

internal/explain/select.go

@@ -300,8 +300,20 @@ func explainSelectWithUnionQuery(sb *strings.Builder, n *ast.SelectWithUnionQuer
 	selects := simplifyUnionSelects(n.Selects)
 	// Wrap selects in ExpressionList
 	fmt.Fprintf(sb, "%s ExpressionList (children %d)\n", indent, len(selects))
-	for _, sel := range selects {
-		Node(sb, sel, depth+2)
+
+	// Check if first operand has a WITH clause to be inherited by subsequent operands
+	var inheritedWith []ast.Expression
+	if len(selects) > 0 {
+		inheritedWith = extractWithClause(selects[0])
+	}
+
+	for i, sel := range selects {
+		if i > 0 && len(inheritedWith) > 0 {
+			// Subsequent operands inherit the WITH clause from the first operand
+			explainSelectQueryWithInheritedWith(sb, sel, inheritedWith, depth+2)
+		} else {
+			Node(sb, sel, depth+2)
+		}
 	}
 	// INTO OUTFILE clause - check if any SelectQuery has IntoOutfile set
 	for _, sel := range n.Selects {

parser/testdata/01236_graphite_mt/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}

parser/testdata/01515_with_global_and_with_propagation/metadata.json

@@ -1,6 +1 @@
-{
-  "explain_todo": {
-    "stmt11": true,
-    "stmt5": true
-  }
-}
+{}

parser/testdata/03033_analyzer_resolve_from_parent_scope/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}

parser/testdata/03611_uniqExact_bug/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt2": true
-  }
-}
+{}

parser/testdata/03671_pk_in_subquery_context_expired/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt7": true
-  }
-}
+{}