Clean up stream resources in Teslemetry config entry unloading

[Bre77]

Proposed change

This PR addresses the config-entry-unloading quality scale item for the Teslemetry integration.

The async_unload_entry function now properly cleans up resources when the config entry is unloaded:

• Calls remove_listener() for each vehicle to unsubscribe from TeslemetryStream events
• Closes the TeslemetryStream WebSocket connection via stream.close()

Previously, the function only unloaded platforms without cleaning up the stream connection and listeners, which could lead to resource leaks.

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:
• Link to documentation pull request:
• Link to developer documentation pull request:
• Link to frontend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.