fix: double-parentheses for boolean cast in index suggestions

PostgreSQL requires double parentheses around cast expressions in
CREATE INDEX: `((expr)::boolean)` not `(expr)::boolean`.

The generated DDL failed with:
  syntax error at or near "::"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jensens

src/plone/pgcatalog/suggestions.py

@@ -73,7 +73,7 @@ def _btree_expr(field, idx_type):
     if idx_type == IndexType.DATE:
         return f"pgcatalog_to_timestamptz(idx->>'{field}')"
     if idx_type == IndexType.BOOLEAN:
-        return f"(idx->>'{field}')::boolean"
+        return f"((idx->>'{field}')::boolean)"
     if idx_type == IndexType.PATH:
         return f"(idx->>'{field}') text_pattern_ops"
     # FIELD, UUID — plain text expression

tests/test_suggestions.py

@@ -90,7 +90,7 @@ def test_boolean_uses_cast(self):
         registry = _reg(is_folderish=IndexType.BOOLEAN)
         result = suggest_indexes(["is_folderish"], registry, {})
         new = [s for s in result if s["status"] == "new"]
-        assert any("::boolean" in s["ddl"] for s in new)
+        assert any("((idx->>'is_folderish')::boolean)" in s["ddl"] for s in new)
 
     def test_uuid_uses_text_expression(self):
         registry = _reg(UID=IndexType.UUID)