test: add non-shell script tests

[muzimuzhi]

Fixes the shebangs in two JavaScript examples added by #377, and add usage tests for them.

Note that no --help tests were added, due to

• Cannot print help of non-shell scripts #405

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.40%. Comparing base (6fd62b4) to head (967b94e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #406      +/-   ##
==========================================
+ Coverage   57.22%   57.40%   +0.18%     
==========================================
  Files          47       47              
  Lines        5543     5543              
  Branches     5543     5543              
==========================================
+ Hits         3172     3182      +10     
+ Misses       1337     1308      -29     
- Partials     1034     1053      +19     

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[Copilot]

Pull request overview

This PR fixes the shebangs in two JavaScript example files and adds corresponding test coverage for non-shell script usage parsing. The changes correct the shebang from #!/usr/bin/env -S usage node to #!/usr/bin/env -S usage exec node to properly use the usage exec subcommand, and add execution tests to verify both the new bracketed syntax (// [USAGE]) and old syntax (//USAGE) work correctly with JavaScript files.

Key Changes

• Fixed shebangs in JavaScript examples to use usage exec node instead of usage node
• Updated comments in example files to clarify they are "non-shell script" tests
• Added two new test functions to verify JavaScript example execution

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
examples/test-usage-double-slash.js	Fixed shebang to use usage exec node and updated comment to specify "non-shell script"
examples/test-usage-double-slash-old.js	Fixed shebang to use usage exec node and updated comment to specify "non-shell script"
cli/tests/examples.rs	Added two execution tests for the JavaScript examples, verifying both new bracketed and old USAGE syntax

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