WasmFS: Add nanosecond support to WasmFS

[jameshu15869]

This PR adds nanosecond support for file times in WasmFS, specifically when used for utime and stat. This PR was separated from #19561 (comment), reusing the same tests.

[tlively]

It looks like the diff still contains changes from #19561. If you change the target branch for this PR from main to jameshu15869:library-wasmfs-utime, that would fix the diff. Although it looks like that branch is in your fork, so this probably isn't possible, unfortunately. We'll have to wait until #19561 is merged to get a reasonable diff here.

[jameshu15869]

Ah I see. For this PR, I did git checkout -b on my old (combined) branch before manually undoing the nanosecond changes on #19561. Is there a better way to do this in the future?

[tlively]

One way would be to add a commit undoing the changes on the original PR, then fork a new branch off of it, then revert the undoing of the changes on the new branch so that the revert commit actually reapplies the changes. Then even if the diff for the PR that adds the changes includes everything, we can just look at the diff for that revert commit to see only the new changes.

[kripken]

this TODO can be removed now

[kripken]

Code lgtm but we have some failures on main it seems, that are showing up here and everywhere else. Work is ongoing to fix those but this will need to wait to land on that.

[sbc100]

Rebasing or merging should fix the CI issues.