Fixes and clean-ups

Hi,

This PR:

• Solves a couple of FIXME items from the tests.
• Improves cleanup in WatchFileCancelable.
• Cleans up the go.mod file with go mod tidy (some deps were not in the go.mod file, etc.); all tests pass; still, let me know if that might potentially be an issue.
• Adds to .gitignore the artifacts generated by make dev.

Cheers!