chore: track uv.lock for reproducible installs

[javier-alvarez]

Summary

• Remove uv.lock from .gitignore and commit the lockfile so dependency resolution is reproducible across dev machines and CI.
• Adjust three queue producers (kafka.py, rabbitmq.py, redis.py) to satisfy pyright's stricter narrowing in 1.1.409.

Why the queue files changed

The committed uv.lock pins pyright==1.1.409, which is stricter about narrowing Any-typed instance attributes. Each producer uses a lazy-start pattern:

self._producer: Any = None
...
async def publish(...):
    if self._producer is None:
        await self.start()      # mutates self._producer
    await self._producer.send_and_wait(...)  # pyright: still narrowed to None here

Pyright 1.1.409 narrows self._producer to None inside the is None branch and does not re-broaden across the intervening await self.start() call (it can't see that start() reassigns the attribute), so it reports reportOptionalMemberAccess on the subsequent member access. The runtime behavior is correct; the limitation is in pyright's flow analysis.

Fix: after the lazy-start block, alias the attribute into a local Any variable and use that. No behavior change.

Test plan

• uv sync --extra dev --extra studio resolves cleanly from the committed lockfile
• uv run pyright → 0 errors
• uv run ruff check . && uv run ruff format --check . pass
• uv run pytest tests/test_exposure/test_queues.py → 6 passed
• CI passes