## Summary
`std::time::now` isn't available on `wasm32-unknown-unknown` but it is
used by `FileTime::now`.
This PR replaces the usages of `FileTime::now` with a target specific
helper function that we already had in the memory file system.
Fixes https://github.com/astral-sh/ruff/issues/16966
## Test Plan
Tested that the playground no longer crash when adding an extra-path
