fix(tests): make the sim backoff test deterministic across platforms

[dieterolson]

What does this PR do?

Makes test_backoff_progression_capped deterministic: the socket in openflight.sim.transport is monkeypatched to refuse connections instantly, and the test polls for the retries it asserts on instead of sleeping a fixed 0.5 s. Also applies ruff's mechanical import-block fix to this file (pre-existing I001/F401 that the pre-commit hook enforces on any touch).

Why was this required?

The test dialed a real socket at 127.0.0.1:1 and slept 0.5 s, then asserted at least two retries had happened. How fast the OS refuses that connect is platform-dependent — on Windows it's slow enough that fewer than two retries land inside the window, so the test fails on every stock Windows checkout (and is timing-sensitive everywhere). The subject under test is the client's backoff schedule, not the platform's TCP stack; the fake socket exercises the same _try_connect failure path (settimeout → connect raises OSError subclass → close) without the platform dependence.

Automated tests

Test-only change: tests/test_sim_transport.py 22/22 on Windows (previously 21/1). The poll loop bounds the wait at 3 s but typically completes in well under half a second.

Manual (human) testing

• Reproduced the flake on Windows 11 (fixed sleep captured < 2 retries) before the change.
• After: ran the single test repeatedly and the full module — green each time; verified the fake implements exactly the socket surface _try_connect uses so the production failure path (log + close + backoff) still executes.

Checklist

• Single feature/fix — this PR is scoped to one thing with a clear story above
• Automated tests included — test-only change; the module is the coverage
• Manual testing described — I documented what I verified by hand above
• Python tests pass (uv run pytest tests/ -v)
• Pylint passes (uv run pylint src/openflight/ --fail-under=9)
• Ruff passes (uv run ruff check src/openflight/)
• UI builds (cd ui && npm run build) — not applicable, no UI changes
• UI lint passes (cd ui && npm run lint) — not applicable, no UI changes
• Updated docs or CHANGELOG if needed — test-only, no changelog entry
• No unrelated changes mixed in