Feat: Add ExtraFields support to OpenAI providers for custom parameters

[Jesssullivan]

This PR adds ExtraFields support to Fantasy's openai and openaicompat providers, enabling custom parameters for OpenAI-compatible APIs that require fields beyond the standard OpenAI specification.

Changes

Added ExtraFields map[string]any to ProviderOptions in both providers:

• providers/openai/provider_options.go
• providers/openaicompat/provider_options.go

The extra fields are applied via params.SetExtraFields() in the respective hook functions:

• providers/openai/language_model_hooks.go
• providers/openaicompat/language_model_hooks.go

Use Case: Z.AI GLM Thinking Mode

This enables passing custom parameters like Z.AI GLM's thinking mode configuration:

providerOptions := &openaicompat.ProviderOptions{
    ExtraFields: map[string]any{
        "thinking": map[string]any{
            "type":          "enabled",
            "budget_tokens": 26214,
        },
    },
}

The extra fields are passed through to the OpenAI SDK's SetExtraFields() method and included in the HTTP request to the provider API.

Dependencies

Depends on: #41 (ZAI provider support)

Related

Relates to: charmbracelet/crush#1295 - Integration in Crush

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• I have read CONTRIBUTING.md.
• I have created a discussion that was approved by a maintainer (for new features).

[kujtimiihoxha]

Hey @Jesssullivan I think I already have it setup to work as expected in crush charmbracelet/crush@6bb85dc#diff-53bdf62a2aac11b071b4d3138352d3e902a49cf41c52ed86bf68d39177a86ebdR529

I just pushed a commit today.

[Jesssullivan]

Hey @Jesssullivan I think I already have it setup to work as expected in crush charmbracelet/crush@6bb85dc#diff-53bdf62a2aac11b071b4d3138352d3e902a49cf41c52ed86bf68d39177a86ebdR529

I just pushed a commit today.

Rad! thanks. I think these are complimentary additions actually, though I may be wrong (still wending around the Fantasy layer). In charmbracelet/crush@6bb85dc#diff-53bdf62a2aac11b071b4d3138352d3e902a49cf41c52ed86bf68d39177a86ebdR529, openaisdk.WithJSONSet() can inject JSON fields directly into SDK requests. This would mean these injections occur on provider creation, not per call.

In this PR, we're adding a discreet ExtraFields mechanism, which works per-call rather than just at provider creation.