Escape single quotes in function aliases for EXPLAIN output

Add escapeFunctionAlias function that only escapes single quotes (not
backslashes) for function aliases. This differs from escapeAlias (used
for column aliases) which also escapes backslashes.

ClickHouse EXPLAIN AST preserves backslashes in function aliases but
requires single quotes to be escaped.

Fixes test: 02915_analyzer_fuzz_1/stmt2

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

internal/explain/functions.go

@@ -7,6 +7,13 @@ import (
 	"github.com/sqlc-dev/doubleclick/ast"
 )
 
+// escapeFunctionAlias escapes single quotes in function alias names.
+// Unlike escapeAlias (for column aliases), this does NOT escape backslashes
+// since ClickHouse EXPLAIN AST preserves backslashes in function aliases.
+func escapeFunctionAlias(alias string) string {
+	return strings.ReplaceAll(alias, "'", "\\'")
+}
+
 // normalizeIntervalUnit converts interval units to title-cased singular form
 // e.g., "years" -> "Year", "MONTH" -> "Month", "days" -> "Day"
 // Also handles SQL standard abbreviations: QQ -> Quarter, YY -> Year, MM -> Month, etc.
@@ -132,7 +139,7 @@ func explainFunctionCallWithAlias(sb *strings.Builder, n *ast.FunctionCall, alia
 		fnName = fnName + "If"
 	}
 	if alias != "" {
-		fmt.Fprintf(sb, "%sFunction %s (alias %s) (children %d)\n", indent, fnName, alias, children)
+		fmt.Fprintf(sb, "%sFunction %s (alias %s) (children %d)\n", indent, fnName, escapeFunctionAlias(alias), children)
 	} else {
 		fmt.Fprintf(sb, "%sFunction %s (children %d)\n", indent, fnName, children)
 	}

parser/testdata/02915_analyzer_fuzz_1/metadata.json

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