Handle parenthesized literals in nested arrays for EXPLAIN output

When arrays contain parenthesized literals like [[((NULL))]], they should
be rendered as nested Function array calls, not as Literal Array format.

Update containsNonLiteralExpressions to detect parenthesized literals
so nested arrays containing them use the correct Function array format.

Fixes tests:
- 01621_summap_check_types/stmt4
- 01635_sum_map_fuzz/stmt4

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

Author: kyleconroy

internal/explain/expressions.go

@@ -305,9 +305,14 @@ func containsOnlyArraysOrTuples(exprs []ast.Expression) bool {
 
 // containsNonLiteralExpressions checks if a slice of expressions contains
 // any non-literal expressions (identifiers, function calls, etc.)
+// or parenthesized literals (which need Function array format)
 func containsNonLiteralExpressions(exprs []ast.Expression) bool {
 	for _, e := range exprs {
-		if _, ok := e.(*ast.Literal); ok {
+		if lit, ok := e.(*ast.Literal); ok {
+			// Parenthesized literals need Function array format
+			if lit.Parenthesized {
+				return true
+			}
 			continue
 		}
 		// Unary minus of a literal (negative number) is also acceptable

parser/testdata/01621_summap_check_types/metadata.json

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

parser/testdata/01635_sum_map_fuzz/metadata.json

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