test: cover manager.py uncovered branches

[bluetoothbot]

What

Six targeted unit tests for previously-uncovered branches in BluetoothManager.
No production code touched.

Why

manager.py sat at 91% line coverage with a long tail of trivially-reachable
branches that nothing in the suite exercised: the connectable=False arms of
the count / address-present / track-unavailable helpers, the unknown-source
short-circuit in async_current_allocations, the early-return when
_async_recover_failed_adapters re-enters with the lock held, and the
cached=False refresh path on async_get_bluetooth_adapters. They're cheap
to cover and they regress silently if anyone reshapes the helpers.

Complements #424 (which targets scanner.py error paths).

How

• test_async_scanner_count_includes_non_connectable — registers one of each,
  asserts connectable=True vs False totals diverge.
• test_async_address_present_non_connectable_history — injects a
  non-connectable advertisement and asserts the all-history branch.
• test_async_track_unavailable_connectable_branch — the only existing
  callers used connectable=False; this hits the True arm and verifies
  the callback lands in _connectable_unavailable_callbacks.
• test_async_current_allocations_unknown_source_returns_empty — [] vs
  None for a missing source.
• test_async_recover_failed_adapters_skips_when_lock_held — pre-acquires
  the recovery lock, asserts async_get_bluetooth_adapters is not called.
• test_async_get_bluetooth_adapters_cached_false_triggers_refresh — patches
  _bluetooth_adapters.refresh and asserts cached=False awaits it.

Testing

• SKIP_CYTHON=1 poetry run pytest tests/ -W "error::DeprecationWarning" -W "ignore::DeprecationWarning:asyncio" → 249 passed, 1 skipped.
• manager.py coverage 91% → 94%; total 95% → 96%.

🤖 Generated with Claude Code

---

Quality Report

Changes: 1 file changed, 83 insertions(+)

Code scan: clean

Tests: failed (FAILED)

Branch hygiene: clean

Generated by Kōan post-mission quality pipeline

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.92%. Comparing base (32db633) to head (b7225f0).
⚠️ Report is 195 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #425      +/-   ##
==========================================
+ Coverage   95.19%   95.92%   +0.73%     
==========================================
  Files          14       14              
  Lines        1913     1913              
  Branches      232      232              
==========================================
+ Hits         1821     1835      +14     
+ Misses         53       42      -11     
+ Partials       39       36       -3     

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[codspeed-hq]

Merging this PR will not alter performance

✅ 11 untouched benchmarks

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_{Comparing koan/cover-manager-uncovered-branches (b7225f0) with main (32db633)}