Fix mypy type errors exposed by py.typed marker

[johanzander]

Summary

• Fixes all 30 mypy type errors that consumers would encounter now that py.typed is shipped (Add PEP 561 typing to enable static type checking for consumers #147)
• Adds a mypy CI workflow to prevent type regressions going forward
• No behavioral changes — all fixes are annotations, type narrowing, and structural improvements

What was fixed

Category	Count	Fix
dict[str, object] inference in params dicts	8	Explicit dict[str, str | int] annotations
union-attr / operator on Optional dates	8	Simplified None-narrowing with sequential if
dict-item in dict unpacking with union types	3	Proper isinstance narrowing with else branch
override (V1 API intentionally changes signatures)	3	# type: ignore[override]
dict-item for session hooks	1	Wrap hook function in list
return-value for process_response	1	Return type Any (.get() can return None)
arg-type for mode_names.get(None)	1	Guard against None key

CI workflow

Added .github/workflows/mypy.yml — runs mypy --ignore-missing-imports on every push and PR, matching the existing ruff workflow. This ensures the py.typed marker remains meaningful by keeping the package mypy-clean.

Why this matters

PR #147 added the PEP 561 py.typed marker, which signals to type checkers that this package ships type hints. Without clean types, consumers running mypy see errors from inside the library that they cannot fix — arguably worse than not shipping py.typed at all.

Test plan

• mypy --ignore-missing-imports passes with 0 errors (was 30)
• ruff check passes
• Runtime smoke test — all imports, instantiation, and hash_password work correctly
• No public API changes — all fixes are internal

🤖 Generated with Claude Code

[johanzander]

another typing improvement @indykoning, building on #147

[indykoning]

Looks good!