[codex] fix deepseek thinking config for streams

[k8scat]

Summary

• forward DeepSeek ThinkingConfig into stream chat completion requests
• add regression coverage for stream requests carrying thinking config

Root Cause

generateStreamRequest builds a stream request from the non-stream request but did not copy the Thinking field, so ChatModelConfig.ThinkingConfig was applied to Generate but dropped for Stream.

Validation

• git diff --check main...HEAD
• GOTOOLCHAIN=go1.24.1 go test ./... -count=1 -gcflags="all=-N -l" in components/model/deepseek

Fixes #807

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

Fixes a DeepSeek streaming bug where ThinkingConfig was applied to non-stream Generate requests but inadvertently dropped from Stream requests.

Changes:

• Forward Thinking from the non-stream request into deepseek.StreamChatCompletionRequest in generateStreamRequest.
• Add a regression test ensuring stream requests carry the ThinkingConfig.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
components/model/deepseek/deepseek.go	Copies Thinking into the stream request so DeepSeek “thinking mode” is preserved for streaming.
components/model/deepseek/deepseek_test.go	Adds a regression test that captures the stream request and asserts Thinking.Type is forwarded.

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[k8scat]

@JonXSnow 大佬帮忙review下