Replace mock-fs with memfs

[ookkoouu]

Description

mock-fs doesn't work on NodeJS 20, use memfs instead.
https://github.com/streamich/memfs

All tests passed in NodeJS 22.9.0.

Implementation Notes

• mock fs fs/promises in all tests
  • use tests/utils/actual-fs when the original fs is needed, such as loading test data
• removed yazl, use adm-zip
  • yazl was used to create a dummy zip file, but the tests timed out, so it was replaced with adm-zip, which has a synchronous method available.

Checklist

• Added unit tests for every exported function/class.
• Added JSDoc to every public function/class/class member.
• Added relevant information to the README.

[Kira-NT]

Thanks for being an absolute MVP! :D
I haven't started working on the tests yet, so I really appreciate you making this part easier for me!