Enhance expression evaluation and update event sheet resources

[Lexian-droid]

This pull request introduces significant improvements to the FKExpressionEvaluator in FlowKit, primarily adding type validation to expression evaluation and updating event sheet resources to use explicit string quoting for literal values. The evaluator now validates result types against expected types, and event sheet .tres files have been updated for consistency with the new evaluation logic.

Core Expression Evaluation Improvements

• The evaluate function in expression_evaluator.gd now takes an optional expected_type parameter, validating the result type after evaluation. If the type does not match, an error is pushed. The evaluation no longer falls back to returning the raw string if evaluation fails, but instead returns null and logs an error. [1] [2]
• Literal and expression parsing functions (_try_parse_literal, _evaluate_expression) now return [found: bool, value: Variant] arrays to distinguish between "not found" and "found with null value" cases, improving reliability and error handling. [1] [2] [3]
• Added utility functions: _check_type for validating result types, and type_name_to_variant_type for mapping string type names to Godot Variant types.

Bulk Event Sheet Updates for Literal Quoting

• Updated all relevant .tres event sheet files to wrap string literal values in quotes (e.g., "windowed" instead of windowed) for keys such as "Mode", "Name", "color", "message", "Key", etc., ensuring they are parsed as string literals under the new evaluation logic. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25]

API Enhancements

• The evaluate_inputs function now accepts an optional type_hints dictionary, allowing per-input type validation during batch evaluation.

These changes improve the safety, predictability, and clarity of expression evaluation in FlowKit, and ensure event sheet resources are compatible with stricter type handling.