Replace fixed-duration sleeps after bus events with gather

[agners]

Proposed change

Several tests use await asyncio.sleep(...) to "wait for the listener to run" after firing a bus event. The fixed duration is real wall-clock time and the wait can be indeterministic — if the handler chain happens to need slightly more time on a busy CI runner, the assertion races the handler.

Bus.fire_event returns the listener tasks since #6252; capture and await asyncio.gather(*tasks) instead of sleeping. Touches test_bus.py (the bus tests were poking scheduling instead of verifying their assertions), test_home_assistant_watchdog.py, test_plugin_base.py, addons/test_manager.py, docker/test_addon.py, and test_store_execute_reload.py.

Other cleanups in the same spirit:

• _fire_test_event in addons/test_addon.py becomes async def and gathers the listener tasks itself, so its 17 call sites collapse to a single await _fire_test_event(...).
• The two test_store_execute_reload.py sites that used the private _update_connectivity() helper are reworked to set the cached connectivity flag directly and fire the event themselves so they can gather the listener tasks the same way.
• The two sleep(1) post-pull drains in docker/test_interface.py collapse to sleep(0) (handler tasks are already gathered inside pull_image), saving ~2s.
• The sleep(0.01) waits inside container_events() task bodies (api/test_addons.py, api/test_store.py, backups/test_manager.py) are just one-yield-to-the-parent and become sleep(0).

Switching to gather exposes a few latent test mocks that were silently swallowing TypeErrors as background-task failures before: CGroup.add_devices_allowed is async def but was patched as a plain MagicMock in docker/test_addon.py (now new_callable=AsyncMock), and the watchdog does await (await self.start()) / await (await self.restart()) because App.start / App.restart return asyncio.Task — the mocks in addons/test_addon.py (test_app_watchdog, test_watchdog_on_stop, test_watchdog_during_attach) needed AsyncMock(return_value=<settled future>) to mirror that shape rather than a plain MagicMock.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionality to the supervisor)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:
• Link to cli pull request:
• Link to client library pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Ruff (ruff format supervisor tests)
• Tests have been added to verify that the new code works.

If API endpoints or add-on configuration are added/changed:

• Documentation added/updated for developers.home-assistant.io
• CLI updated (if necessary)
• Client library updated (if necessary)

[mdegat01]

Could consider moving this to tests.common and making it a generic helper that accepts event, data and awaits the task. So we can use it in all the places shown.

[mdegat01]

Good call. I really hated those sleeps, especially the ones that had to be > 0 to make the test work, much better 👍