feat(ble-proxy): pluggable connect_strategy hook for MatterBleProxy

[Apollon77]

Summary

• Adds an optional connect_strategy callable to MatterBleProxy so embedders can plug in bleak_retry_connector.establish_connection (or any other connection helper) without making it a hard dependency of the library.
• New public helper matter_ble_proxy.default_connect_strategy(target, on_disconnect, timeout_ms) keeps the plain-Bleak behavior for the standalone CLI.
• _handle_connect delegates to the strategy; existing TimeoutError / generic-Exception → connection_failed mapping is preserved, so error semantics on the wire don't change.

Generic hook, not HA-specific. Connection establishment is already the library's responsibility (_handle_connect constructs the BleakClient and calls .connect()); the hook makes that one step pluggable so any embedder — bleak-retry-connector users, custom connection pools, telemetry wrappers — can supply their own helper. Home Assistant is the first consumer; the library stays dependency-free.

Why

Home Assistant's habluetooth.wrappers warns whenever BleakClient.connect() runs outside bleak_retry_connector.establish_connection. During BLE proxy pairing through HA you see:

habluetooth.wrappers C8:8B:A4:F7:57:32: BleakClient.connect() called without
  bleak-retry-connector. For reliable connection establishment, use
  bleak_retry_connector.establish_connection().

Functionally pairing succeeds, but we lose adapter path scoring + the retry policy HA uses everywhere else. With this hook the HA integration can pass establish_connection while the library stays Bleak-only.

Strategy contract

ConnectStrategy = Callable[
    [BLEDevice | str, Callable[[BleakClient], None], int],
    Awaitable[BleakClient],
]

Strategy receives (target, disconnected_callback, timeout_ms) and returns a connected BleakClient. The library applies no extra timeout — the strategy owns its retry/timeout policy.

Follow-up

The Home Assistant matter integration PR (home-assistant/core#171384) will pin to the released version of this change and pass an establish_connection-backed strategy from homeassistant/components/matter/ble_proxy.py.

Test plan

• npm run python-ble-proxy:lint
• npm run python-ble-proxy:typecheck
• npm run python-ble-proxy:test (12 passed, including 6 new in test_connect_strategy.py)
• npm run python-ble-proxy:build
• Real-device pairing through HA against a 0.7.2 build of the library — verifies the warning is gone end to end (deferred to the HA-side PR once the lib release is out)

[Copilot]

Pull request overview

Adds a pluggable BLE connection hook to the Python BLE proxy client so embedders (notably Home Assistant) can supply a custom connection-establishment routine (e.g., bleak_retry_connector.establish_connection) without introducing a hard dependency, while keeping the existing on-the-wire error semantics intact.

Changes:

• Introduces connect_strategy (optional) on MatterBleProxy, defaulting to a new default_connect_strategy.
• Refactors _handle_connect to delegate connection establishment to the selected strategy while preserving TimeoutError / generic exception → connection_failed mappings.
• Adds unit tests covering default vs custom strategy behavior and error mapping.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
python_ble_proxy/matter_ble_proxy/client.py	Adds default_connect_strategy, threads optional connect_strategy through MatterBleProxy, and delegates _handle_connect to it while keeping existing error mapping.
python_ble_proxy/matter_ble_proxy/init.py	Exposes default_connect_strategy as part of the public package API.
python_ble_proxy/tests/test_connect_strategy.py	Adds unit tests validating strategy wiring, invocation, and error mapping behavior.