Proposed change

This PR fixes an issue in the August integration where a generic ValueError was raised when the OAuth implementation was not available during startup (e.g., due to network issues). The error message "Implementation not available" was not user-friendly and prevented proper retry logic from executing.

The fix catches the ValueError from async_get_config_entry_implementation() and converts it to ConfigEntryNotReady with a descriptive message. This allows Home Assistant to automatically retry the setup later when the OAuth implementation becomes available.

ERROR (MainThread) [homeassistant.config_entries] Error setting up entry 89atl@koston.org for august
Traceback (most recent call last):
  ...
  File "/usr/src/homeassistant/homeassistant/helpers/config_entry_oauth2_flow.py", line 581, in async_get_config_entry_implementation
    raise ValueError("Implementation not available")
ValueError: Implementation not available

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
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• Link to frontend pull request:

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