fix: don't flap a lock_offline repair during integration startup (#1257)

[raman325]

Proposed change

Closes the repair-issue flapping in #1257: after a Home Assistant restart, Lock Code Manager begins polling/writing before the lock's underlying integration has finished starting up. For Matter this surfaces as transient InvalidState: Not connected errors. Those failures feed the lock circuit breaker, and at POLL_FAILURE_ALERT_THRESHOLD (12) consecutive failures the coordinator raises the lock_offline repair — which is then auto-cleared the instant the integration finishes loading. The repair is created and dismissed entirely within the startup window, so the user sees a repair appear and vanish for a lock that was never actually offline.

Fix

A lock that has never been reached is not "offline" — "offline" presupposes it was once online. The coordinator now tracks _reached_once (set on the first successful poll/push, in _reset_backoff) and only raises lock_offline once the lock has actually been reached:

• Startup window (never reached, integration still loading): transient failures accumulate on the breaker as before, but no lock_offline repair is raised — nothing to flap.
• Genuine outage (reached, then drops): _reached_once is True, so a sustained failure raises lock_offline exactly as it does today, and recovery clears it.

Relationship to #1258 / #1257

#1258 (released in 4.0.6) already reclassified the underlying transient Matter startup errors (unknown(133), InvalidState: Not connected) from fatal (CodeRejectedError → disable slot / unexpected error → suspend slot) to the retry path (LockDisconnected). That stopped the slot_disabled / slot_suspended repairs. But it rerouted those same failures into the connectivity breaker, which is what feeds lock_offline — so the flap moved there. This PR closes that remaining startup-window repair.

This is unrelated to the verified-credential lifecycle work (#1259) and branches off main.

Type of change

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

Additional information

• A previously-reachable lock that goes offline still alerts; only a never-yet-reached lock is suppressed (such a lock is "still starting up / misconfigured", surfaced by its own entity being unavailable and slots not syncing, not by a spurious "offline" repair).
• Full Python suite green (1251). New tests: lock_offline not created when never reached (even past the threshold); created normally after a reach-then-drop; push_update marks the lock reached. The four existing lock_offline threshold tests were updated to establish a prior reach, reflecting the new semantic.
• Accepted trade-off: _reached_once is per-coordinator in-memory state. A lock that is dead across an HA-restart boundary and is never reached afterward will not raise lock_offline (it was never "online" this session). This is intentional — it's the startup-flap fix — and is surfaced instead by the lock entity being unavailable and slots not syncing.
• Fixes [ISSUE] Matter lock slots disabled after HA restart due to startup credential sync failures #1257.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.15%. Comparing base (ebac273) to head (e8330cc).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1260   +/-   ##
=======================================
  Coverage   97.15%   97.15%           
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  Files          54       54           
  Lines        6434     6437    +3     
  Branches      461      461           
=======================================
+ Hits         6251     6254    +3     
  Misses        183      183           

Flag	Coverage Δ
python	97.71% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...components/lock_code_manager/domain/coordinator.py	96.63% <100.00%> (+0.08%)	⬆️

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