fix: prevent postinstall script from running when installed as dependency using pnpm

[sternma]

The postinstall script runs patch-package even when the package is installed as a dependency, causing installation failures for users who don't have patch-package installed in their projects. This issue is particularly evident when using pnpm, which handles module isolation more strictly.

Problem:
The postinstall script attempts to run patch-package, which isn't available in user projects, causing installation to fail. The workaround is for the user to add patch-package as a top-level dev-dependency in their own project.

Solution:
This fix updates patches/patch.js to check if the script is running inside a node_modules directory. If it is, the script assumes it's being installed as a dependency and skips running patch-package.

Compatibility:
Tested with npm, pnpm, and yarn. The fix works across all package managers.

Testing:

• Verified that postinstall runs during local development.
• Confirmed that installation succeeds without errors in a test project.

[sternma]

Hey @badeball - I read your proposal in cucumber's repo. Would you still consider completing this PR to unblock pnpm users?

[badeball]

Would you still consider completing this PR to unblock pnpm users?

This would at the very least have to test the mentioned package managers. Preferably using a different jobs to test latest version of each, using one of the examples.

[badeball]

I'm also not a fan of the heuristics implemented here. You're removing the possibility of working inside a node_modules directory. While I don't do this myself, I see no reason for why this library should not allow it.

Edit: Scratch this - as this will exclusively affect developers of the library, ie. me only.

[badeball]

I tried using pnpm to install dependencies of one of the examples (esbuild-cjs) and it runs seemingly fine and without errors. What issue have you observed?