fix(ai-platform): update batch prediction model to gemini-2.5-flash

[angelcaamal]

Description

This PR resolves a blocking 5 NOT_FOUND error encountered during Gemini batch prediction jobs. The static model version gemini-2.0-flash-001 was decommissioned and is no longer available for batch processing.

To fix this, the script has been updated to use the latest stable model (gemini-2.5-flash).

Note: The test suite is currently failing due to external issues unrelated to this PR, but it is already being worked on. However, this specific change has successfully fixed the error in the batch prediction samples test, as evidenced in the screenshot below.

Fixes Internal: b/531820581

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Code Review

This pull request updates the Gemini model version from gemini-2.0-flash-001 to gemini-2.5-flash in the batch prediction code snippets for both BigQuery and Google Cloud Storage. I have no feedback to provide as there are no review comments.

[XrossFox]

LGTM