Enable ruff argument, idiom and pytest-style rules (ARG, B, C4, FBT, PERF, PLW, PT, PTH, RUF, SIM and others)

[anth-volk]

Fixes #3923

Summary

Phase 1 step 1.8, group 8a: arguments, idioms and pytest style. Stacked on #3920. Group 8b follows with the complexity refactors and the switch to select = ["ALL"].

• Unittest exemption (decided for this group): the shared rules tool's tests use unittest on purpose, because the tool needs only the standard library. scripts/rules/tests/** is exempt from ruff's pytest-style rules (PT), registered as api.quality.unittest-ruff-exemptions.
• Rules: select gains ARG, ASYNC, B, C4, FBT, PD, PERF, PGH, PLW, PT, PTH, RUF and SIM. All 912 findings are fixed or kept with an inline reason, one commit per family.
• Unused arguments (ARG, 468):
  • 118 tests now request side-effect fixtures with @pytest.mark.usefixtures; the collected test IDs are identical.
  • Unused *args/**kwargs became *_args/**_kwargs. A named lambda or callback parameter is underscored only where every caller passes it positionally.
  • The rest keep their names with a reason: methods that implement a protocol or override a base method (typing.override needs Python 3.12), Flask views that receive URL variables by keyword, fakes called by keyword, and SQLAlchemy and Alembic hooks.
• Keyword-only booleans (FBT): PolicyEngineCountry.calculate and prepare_calculation (spm_requested, prepared), EconomyService._setup_sim_options, and the cache backend protocol's pipeline(*, transaction=True). Every caller already passed these by keyword. The FastAPI current query parameter and Alembic's positional include_object hook are kept, with reasons.
• Bugbear (B):
  • B904: the simulation and report-output routes' create and update handlers now raise BadRequest(...) from e. The 400 responses are unchanged; only the traceback's chaining text changes.
  • B905: zip(..., strict=True) where the lengths are fixed by literals.
  • B023: loop variables bound in closures that only run within their own iteration.
• Idioms: 154 dict() calls become literals, plus comprehensions (C4, PERF), simplified conditions and combined with statements in the same order (SIM), ClassVar annotations, explicit Optional types, raw regex patterns and sorted __all__ (RUF), Path.open (PTH) and check=False on subprocess.run (PLW1510).
• Pytest style (PT): 37 pytest.raises gain match= with the real message; where a test only asserted that text separately, the match replaces that assertion. Parametrize names and values use tuples and lists, and composite assertions are split.
• Kept with a reason:
  • try/except blocks: the 19 blocks that groups 5 and 6 kept deliberately stay try/except (SIM105 on the try: line, with the handler's reason). Two others became contextlib.suppress.
  • Module-level state that tests patch: the Cloud SQL, v2 engine and readiness globals (PLW0603).
  • Non-ASCII digits under test: RUF001.
  • .values: MicroSeries and a pandas extension array, where .to_numpy() would differ (PD011).
  • A single startup read in an async function: ASYNC240.
• Registry: api.quality.ruff-lint now lists the 13 families. The shared rules tool changed (comprehensions, check=False, a bound loop variable and an unused parser parameter removed), so its hash is now 3a3540a5107a; sim takes the same copy in Enable ruff argument, idiom and pytest-style rules (ARG, B, C4, FBT, PERF, PLW, PT, PTH, RUF, SIM and others) policyengine-sim-api#802.

Testing

• The make test set (tests/unit, tests/contract, to_refactor and the dedupe integration test): 2,416 passed, 4 failed, the same as the base today.
  • The 4 failures are a date-dependent test on master. tests/unit/v2/test_stage12_comparison_models.py fixes retention_expires_at at 2026-10-14 but leaves created_at on the real clock, so its inserts fail the retention check since that date. It's unrelated to this PR and needs its own fix against master.
  • With the model clock frozen at 2026-09-20, every test passes on both base and branch.
• make typecheck-v2 is clean. mypy on the 128 changed files outside that gate shows no new errors.
• ruff check and ruff format --check (0.15.12) are clean repo-wide.
• Every Pydantic model schema and adapter, the FastAPI OpenAPI with every native router enabled, the /v2/openapi.json preview and the legacy spec are byte-identical to the base.
• The quality guards, the rules guard and the rules tool unittest (75 tests, also on Python 3.11) pass.
• CI/CD: no workflow changed. .github/find-api-model-versions.py changed only in idioms; it reads only GITHUB_ENV, which the Actions runner provides, and only when run without --shell, which its CI caller always passes.
• CI: this PR is above the bottom of its stack, so it runs only CI complete, which fails and says why. Its full run starts once the PRs below it merge.

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