feat: Add api_key_provider to ModelProviderInfo

[geoah]

I really am not sure what the method definition needs to look like, tried some much simpler approaches that didn't work.
Suggestions are more than welcome.

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[cpluss]

Please remove these - it'll just confuse a rebase and it does not really add any concrete value :)

[cpluss]

If we want a generic trait here let's make it such, rather than an anonymous function

// Note how we can enforce this trait to implement other traits to make it
// compatible, and avoid having to manually implement PartialEq here
trait ApiKeyProvider: Send + Sync + PartialEq + Debug {
     fn get(): String;
}

Then use as such, it's much cleaner, e.g.

pub api_key_provider: Option<dyn ApiKeyProvider>

Might also make sense to not use an Arc here at all, as it's an upstream constraint you're enforcing? Have your trait engage with an arc instead (hold it, own it) :)

--

Another way we could do this btw is to replace the api_key with an enum, e.g.

enum ModelApiKey {
   Provider(dyn ApiKeyProvider);
   Env(string);
}

Not strictly necessary for this hack though

[geoah]

Updated to a trait with arc