fix(genai): resolve module path and naming issues in count-tokens samples

[angelcaamal]

Description

This PR addresses execution errors in the genai/count-tokens test suite.

Changes:

Path Corrections: Updated require statements in test files to correctly point to the corresponding sample source files.

Fixes Internal: b/517253756

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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 test files to align with renamed source files and the standardized countTokens function. A review comment identifies an inconsistency in the require statements where the .js extension was omitted in one file but retained in another, suggesting its restoration for repository-wide consistency.

[XrossFox]

LGTM!

[Kef131]

LGTM