Add Gardena mower protocol features

[AlirezaT]

This ports the generic Automower/Gardena BLE protocol work from the Home Assistant Gardena BLE integration back into the Python library.

Included:

• safer command response helpers that expose mower response results
• serialized locked command flow for multi-step commands
• keep-alive task cleanup on disconnect
• schedule transaction helpers for reading, replacing, and clearing weekly tasks
• Gardena-compatible SpotCut flow: prepare SpotCut, start timed override, then trigger start
• additional protocol definitions for battery diagnostics, SensorControl/frost sensor, drive-past-wire, starting points, reversing distance, SpotCut, realtime sensor data, signal quality, firmware/hardware identity, and production info
• parser support for signed 16-bit values and variable trailing integer fields, so GetTask works with both existing upstream fixtures and Gardena responses

Notes:

• The new commands were tested from the Home Assistant integration against a Gardena Sileno mower and cross-checked with Gardena app BLE/HCI observations where available.
• Some commands are model-dependent and may return NOT_AVAILABLE, INVALID_ID, or NOT_ALLOWED on mowers that do not expose that feature.

Validation:

• python -m unittest discover
• python -m compileall automower_ble tests
• git diff --check