fix(provider): inject chat_template_kwargs for Nvidia NIM deepseek-v4 models

[Zireael]

Issue for this PR

Closes #24264

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Resolves an issue where Nvidia NIM's deepseek-v4-flash and deepseek-v4-pro models fail to return a response when used in OpenCode because the Nvidia NIM API explicitly requires chat_template_kwargs: { enable_thinking: true, thinking: true } in the root of the JSON payload for reasoning models.

Since the Vercel AI SDK strips unknown options, configuring this via opencode.jsonc does not work. This PR fixes the issue by intercepting the fetch request in the nvidia provider definition and manually injecting the required chat_template_kwargs into the JSON body when a deepseek-v4 model is used.

How did you verify your code works?

By locally overriding the provider configuration and confirming that the injected fetch wrapper successfully allows DeepSeek models from the Nvidia NIM API to stream reasoning and text responses.

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[rekram1-node]

isnt it enabled by default tho?

[github-actions]

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