Add full mypy type annotation coverage and restore PEP 561 support

[joe-clickhouse]

The py.typed marker will be removed in 1.0 because annotation coverage wasn't complete enough to fulfill the PEP 561 contract. This issue tracks the work required to get there.

1. Add mypy to CI
2. Complete return type annotations on all public methods, especially the DB-API and SQLAlchemy layers
3. Fill in missing property return types across QueryResult, QuerySummary, and Client
4. Annotate module-level utility functions in common.py, httputil.py, and parser.py
5. Restore py.typed marker and package_data entry once passing cleanly

[yudelevi]

suggest giving https://docs.astral.sh/ty/ a try, it's pretty good

[joe-clickhouse]

Thanks @yudelevi! Great suggestion. I'll consider ty instead of mypy for 1.0.

[cdagraca]

Does this relate to this PR removing py.typed? Because that's causing a pyright validation failure (error: Stub file not found for "clickhouse_connect" (reportMissingTypeStubs)) on updating from 0.14.1 to 0.15.1

[joe-clickhouse]

@cdagraca yes, it was removed in v0.15.0 because the file implied that we did in fact have complete type hints throughout the full public facing API but we do not yet.