fix: add 'limit' event to BusboyFileStream typings

[williamfds]

Closes #173

This PR adds the limit event to the BusboyFileStream typings so that consumers can listen for file‐size limit breaches.
It also includes:

• A unit test (test/file-stream-limit.test.js) that verifies the limit event is emitted.
• Documentation in README.md showing how to use the event.
• tap and @types/tap added to devDependencies to support the new test.

Checklist

• run npm run test
• run npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follow the Developer’s Certificate of Origin and the Code of Conduct

#191 (comment)

[gurgunday]

Why didn't the CI run?