Feature/get gateway status

[hbattat]

This PR adds support for monitoring the status of TTLock Wifi Gateways. It introduces a new binary sensor that reports the online/offline status of each gateway associated with the account.

Fixes #71

[codecov]

Codecov Report

❌ Patch coverage is 90.67797% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.58%. Comparing base (ac7c627) to head (a4cea42).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
tests/test_gateway.py	92.59%	4 Missing ⚠️
custom_components/ttlock/binary_sensor.py	90.62%	3 Missing ⚠️
custom_components/ttlock/api.py	33.33%	2 Missing ⚠️
custom_components/ttlock/coordinator.py	85.71%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #246      +/-   ##
===========================================
+ Coverage    85.25%   85.58%   +0.33%     
===========================================
  Files           22       23       +1     
  Lines         1594     1707     +113     
===========================================
+ Hits          1359     1461     +102     
- Misses         235      246      +11     

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