fix(librarian/nodejs): run eslint directly for formatting

[julieqiu]

Format is updated to run eslint directly instead of npm run fix (gts).

The previous approach of running npm run fix failed because gts expands file globs (like src/**/*.ts) at the shell level. This caused it to pick up and attempt to lint files within the node_modules directory, leading to formatting failures. Running eslint directly with explicit --ignore-pattern node_modules/ ensures that only the generated source files are processed.

Additionally, this switch allows us to use a pre-installed global eslint, avoiding runtime network dependencies and the need for a local npm install during code generation. We use eslint@8 to maintain compatibility with the legacy .eslintrc.json format still used across existing libraries. See #4590 for additional context.

For #4404

[gemini-code-assist]

Code Review

This pull request updates the Node.js formatting to use eslint directly, which is a good improvement to remove network dependencies and fix globbing issues. The implementation is solid, and the accompanying test is thorough. I have a couple of minor suggestions to improve code style and align with the repository's Go guidelines, mainly around error handling patterns in both the implementation and the test code.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.27%. Comparing base (1eadeb4) to head (22a4eeb).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/librarian/nodejs/generate.go	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4592      +/-   ##
==========================================
- Coverage   79.39%   79.27%   -0.13%     
==========================================
  Files         110      110              
  Lines        9223     9235      +12     
==========================================
- Hits         7323     7321       -2     
- Misses       1389     1403      +14     
  Partials      511      511              

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