Providers: Universal Source Generator for tools/functions

[HavenDV]

this part seems weird to me
var service = new BookStoreService();
model.AddGlobalTools(service.AsAnthropicTools(), service.AsAnthropicCalls());
seems like it should be more like model.GetService()

unfortunately I have not yet abstracted the functions, so far this has only been implemented for a few providers, including OpenAI, Antropic and Gemini

They can be in different formats (both in OpenAPI and xml), I would like to have a more universal generator that also has a fallback for any model

[HavenDV]

Closed in #419