fix(sdk): make the Python SDK pass its own strict mypy configuration

[loveRhythm1990]

Summary

pyproject.toml sets strict = true with files = ["src"], but mypy src reported 31 errors in 4 files. Reproduced exactly (mypy 2.4.0, Python 3.12): Found 31 errors in 4 files (checked 11 source files) — matching the issue's count.

Four groups:

Code	Count	Cause	Fix
valid-type	16	Every resource class defines a method named list, shadowing the builtin inside the class body, so adds: list[str] | None resolved to the method	Qualify as builtins.list[...] — renaming the methods would break the public API
no-any-return	7	_request/_arequest return Any, returned straight out of functions declared -> dict[str, Any] (and -> float in _backoff)	Explicit cast; _backoff converts the Any-typed int.__pow__ result
unused-ignore	6	# type: ignore[return-value] comments that never matched the real code (no-any-return)	Removed, along with the casts that make them unnecessary
union-attr	2	snapshots.list built items via data.get("snapshots", data.get("items", [])) — typed Any | None — then iterated it	Build the list defensively

The union-attr pair was a latent runtime bug, not just a typing complaint: an empty body (204) or an explicit null field would have made the comprehension iterate None and raise TypeError.

Test plan

• mypy src → Success: no issues found in 11 source files (was 31 errors)
• pytest tests/unit → 122 passed, no behavior change
• ruff check src → all checks passed; ruff check src tests back to the 7 pre-existing findings that are identical on unmodified main (they come from a newer ruff than the project's >=0.4 floor and all sit in test files)
• Verified annotations still resolve at runtime (BranchesResource.apply → builtins.list[str] | None)

Not done here: the issue also suggests considering running the type check in CI. The release workflow runs unit tests but no type check, and there's no test-sdk-python.yml — adding one changes the PR gate for everyone, so I left that decision to you rather than bundling it into a bug fix. Happy to open a follow-up.

Fixes #266

🤖 Generated with Claude Code

[loveRhythm1990]

Reviewed head 2963d8fc26d41c25620d2e9ed62f2d80820e27ac.

No blocking findings in this revision.

The builtins.list annotations correctly avoid class-scope shadowing by resource methods named list. The explicit numeric conversion and casts address strict typing without changing the intended API results. The snapshot normalization consistently returns an empty list for the supported empty/null forms.

Validation: mypy src passed for all 11 source files, and the existing Python suite passed, 122/122 tests. Additional sync/async mocked checks covered HTTP 204, null snapshots/items, a bare empty list, and an empty snapshots list (10 checks total); runtime resolution of the affected branch annotations also succeeded. Local Python version: 3.14.7.

Coverage: 4/4 changed files reviewed; 0 skipped (100%).

[loveRhythm1990]

lgtm

Re-reviewed 2963d8fc26d41c25620d2e9ed62f2d80820e27ac, unchanged since the previous review. The strict-typing fixes and empty/null snapshot response handling look correct.

Coverage: 4/4 changed files reviewed; 0 skipped (100%). Previous validation on this same head passed mypy for all 11 source files, 122/122 unit tests, and the extra sync/async empty-response checks; these were not rerun in this pass.