Publicly expose OllamaApiClient.Dispose

[Joy-less]

This means that when putting the client in a field/property, you don't have to write code like:

((IDisposable)Client)?.Dispose();

Instead you can just write:

Client?.Dispose();

[awaescher]

Pretty interesting as I am sure this was not possible before because IChatClient was implemented explicitly. And the compiler did not accept a single public implementation for the method. We discussed this earlier (#126).
I guess the compiler got an update here with the latest .NET 9 / Visual Studio updates. Nice. Thanks a lot.