fix: old provider not shutting down when the new provider fails to initialize

[NeaguGeorgiana23]

This PR

Ensures that a displaced feature provider is always shut down when a new provider is set, preventing resource leaks when the new provider fails to initialize.
Previously, the old provider was removed from the internal repository map immediately upon setting a new one, but Shutdown() was only called if the new provider successfully initialized. If the new provider's Init() failed, the old provider remained active but unreferenced, leaking its resources.

Related Issues

Fixes #97

[gemini-code-assist]

Code Review

This pull request modifies the ProviderRepository to unconditionally shut down the old provider during initialization, regardless of whether the new provider successfully reaches a ready state. Correspondingly, the test suite has been updated to verify that the old provider is indeed shut down even when the new provider's initialization fails. I have no feedback to provide.