feat(thinking): add xAI provider support with reasoning.effort implementation

- Implemented `xAI` provider for thinking configurations with support for reasoning.effort levels.
- Registered `xAI` in available providers and updated relevant APIs for compatibility.
- Added unit tests for `xAI` provider functionality, including fallback logic for unsupported levels.
- Integrated `xAI` with executor handling and ensured conformance with OpenAI-compatible standards.

internal/runtime/executor/xai_executor.go

@@ -487,7 +487,7 @@ func (e *XAIExecutor) prepareResponsesRequest(ctx context.Context, req cliproxye
 	body := sdktranslator.TranslateRequest(from, to, baseModel, bytes.Clone(req.Payload), stream)
 
 	var err error
-	body, err = thinking.ApplyThinking(body, req.Model, from.String(), to.String(), e.Identifier())
+	body, err = thinking.ApplyThinking(body, req.Model, from.String(), e.Identifier(), e.Identifier())
 	if err != nil {
 		return nil, err
 	}