Reset update percentage after install

[TheJulianJES]

DRAFT.

Reset update_percentage when a firmware update finishes

The firmware update entity set in_progress back to False when an install completed, failed, or raised, but never cleared update_percentage. This left the entity reporting a stale percentage (typically 100) alongside in_progress == False — an internally inconsistent state at the library boundary.

Home Assistant's update platform happens to mask the percentage (update_percentage if in_progress else None), so an HA frontend user usually doesn't notice. But the ZHA library's own state dict and websocket contract emit the stale value directly, and relying on a downstream consumer to sanitize our output is fragile — the library should report correct state itself.

Fix

The three exit paths (exception, non-SUCCESS status, success) each duplicated self._attr_in_progress = False + maybe_emit_state_changed_event(). These are collapsed into a single finally block that also clears self._attr_update_percentage, so the progress state is always cleared regardless of the update's outcome.

This also fixes a latent bug on cancellation. asyncio.CancelledError is a BaseException, so it was never caught by except Exception, and without a finally the old code skipped cleanup entirely — leaving the entity stuck at in_progress: true / 100% indefinitely. The install call chain is unshielded end to end (HA async_install_with_progress → HA ZHA async_install → this entity → zigpy update_firmware), so a cancelled install task propagates CancelledError straight into this code. This is reachable in practice whenever the install task is cancelled while ZHA keeps running — e.g. an automation with mode: restart re-triggering, automation.reload/script.reload, or a timeout: wrapping update.install. The finally now clears the state and lets the CancelledError propagate untouched.

Tests

• test_firmware_update_success — assert update_percentage is reset to None after a successful install (the primary regression; fails against the old code with assert 100.0 is None).
• test_firmware_update_raises — assert the progress state is cleared after a failed install.
• test_firmware_update_cancelled — new test: a CancelledError from update_firmware propagates untouched (not wrapped in ZHAException) and both in_progress and update_percentage are still cleared.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.29%. Comparing base (a0e3195) to head (f91bf23).
⚠️ Report is 2 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #818      +/-   ##
==========================================
- Coverage   97.29%   97.29%   -0.01%     
==========================================
  Files          55       55              
  Lines       10933    10930       -3     
==========================================
- Hits        10637    10634       -3     
  Misses        296      296              

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