module: fix extensionless entry with explicit type=commonjs

[inoway46]

When an extensionless entry point contains ESM syntax but is in a package with "type": "commonjs" in package.json, the module would silently exit with code 0 without executing or showing any error. This happened because extensionless files skip the .js suffix check in the CJS loader, so the explicit type: commonjs was not being enforced, allowing ESM syntax to be silently delegated to ESM loading which never completed before the process exited.

This change ensures the CJS loader treats extensionless entry points as commonjs when type is explicitly set to "commonjs" in package.json, forcing ESM syntax to surface as a SyntaxError instead of silently exiting.

Fixes: #61104

Related: #61171 (alternative approach)

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[joyeecheung]

Thanks for the PR, a couple of comments, otherwise this looks good.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71228/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.74%. Comparing base (f6464c5) to head (601e4c5).
⚠️ Report is 66 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61600      +/-   ##
==========================================
- Coverage   89.76%   89.74%   -0.03%     
==========================================
  Files         673      675       +2     
  Lines      203944   204511     +567     
  Branches    39191    39305     +114     
==========================================
+ Hits       183080   183540     +460     
- Misses      13194    13248      +54     
- Partials     7670     7723      +53     

Files with missing lines	Coverage Δ
lib/internal/modules/cjs/loader.js	98.36% <100.00%> (+0.19%)	⬆️

... and 60 files with indirect coverage changes

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[inoway46]

Thanks for the approval.
I pushed a small lint follow-up: I added require('../common') at the top of test/es-module/test-extensionless-esm-type-commonjs.js to satisfy the required module ordering rules.

I also verified make lint-js locally for the changed JS files.
Could you please rerun CI if needed? Thank you.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71237/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71255/

[joyeecheung]

@inoway46 Can you squash the commits? I don't think they would pass the test individually.

[inoway46]

I squashed the commits and force-pushed the branch.
The PR now has a single commit: 79d60d5.
Please let me know if you'd like any further changes.