chore: enable mypy checking for source modules

The mypy override was suppressing all errors for both tests and
source code, making the mypy pytest plugin useless. Keep the
suppression for tests only so mypy can catch real issues in the
dialect source.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: splasky

pyproject.toml

@@ -17,5 +17,5 @@ ignore_missing_imports = true
 disable_error_code = ["var-annotated", "import-untyped"]
 
 [[tool.mypy.overrides]]
-module = ["tests.*", "sqlalchemy_datastore.*"]
+module = ["tests.*"]
 ignore_errors = true