fix(open-responses): map non-image file parts to input_file - #15212

…#15259)

This is an automated backport of #15212 to the release-v6.0 branch. FYI
@aayush-kapoor
This backport has conflicts that need to be resolved manually.

### `git cherry-pick` output

```
Auto-merging packages/open-responses/src/responses/convert-to-open-responses-input.test.ts
Auto-merging packages/open-responses/src/responses/convert-to-open-responses-input.ts
CONFLICT (content): Merge conflict in packages/open-responses/src/responses/convert-to-open-responses-input.ts
Auto-merging packages/open-responses/src/responses/open-responses-language-model.test.ts
error: could not apply 52d2e30... fix(open-responses): map non-image file parts to input_file (#15212)
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
```

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Aayush Kapoor <83492835+aayush-kapoor@users.noreply.github.com>

## Background

#13843

file parts that are not images (e.g., application/pdf) are silently
dropped from the request body. The SDK logs a warning (unsupported file
content type), but the resulting API request is sent without the file
data, often causing the model to respond that no document was provided.

The OpenAI Responses API supports non-image files via the input_file
part

## Summary

adds support for non-image file inputs, especially PDFs, by mapping them
to OpenAI Responses input_file parts:

- URL-backed files become `{ type: 'input_file', file_url: '...' }`
- base64/data-backed files become `{ type: 'input_file', filename,
file_data: 'data:<mediaType>;base64,...' }`

## Manual Verification

verified by running the cli examples

## Checklist

- [x] All commits are signed (PRs with unsigned commits cannot be
merged)
- [x] Tests have been added / updated (for bug fixes / features)
- [ ] Documentation has been added / updated (for bug fixes / features)
- [x] A _patch_ changeset for relevant packages has been added (for bug
fixes / features - run `pnpm changeset` in the project root)
- [x] I have reviewed this pull request (self-review)

## Related Issues

fixes #13843 

Co-authored-by: shivamtiwari3
<33183708+shivamtiwari3@users.noreply.github.com>