feat(vast): C 解析器补齐 T | None 与语句级声明

支持 T | None、typedef/define/static/export/extern/inline 变量形态；C 解析失败不再回退纯 Python，直接 fail-fast；同步重建 _parser.pyd。

lib/vast/__init__.py

@@ -183,13 +183,7 @@ def parse(source: str, filename: str = '<unknown>', mode: str = 'exec', *,
         try:
             return _VAST_C_PARSE(source, mode)
         except SyntaxError as _exc:
-            if _os.environ.get('VAST_USE_C') == 'strict':
-                raise _HumanizeSyntaxError(_exc, source, filename) from None
-            _ReportCFallback(filename, _exc)
-        except Exception as _exc:
-            if _os.environ.get('VAST_USE_C') == 'strict':
-                raise
-            _ReportCFallback(filename, _exc)
+            raise _HumanizeSyntaxError(_exc, source, filename) from None
     try:
         return _ParsePure(source, mode)
     except SyntaxError as _exc: