Adding kumo.fs.stat to get file/dir meta data

[kayozaki]

• Adding function to check the stat of a file or directory.

I personally wanted to get the last modified time of a file for the function i'm working on.
other attributes aren't necessarily required, but adding them as it may help others.

[wez]

Looking good! A couple of small changes and I think we're there!

[wez]

A couple of things for these time accessors:

1. We have the nanosecond component available and we can feed that into chrono to get sub-second precision
2. We don't need an Option around either seconds or nanoseconds
3. There's an unwrap that we should avoid in case someone manages to put complete nonsense into time fields (eg: might happen if the fs is corrupt, but might also be possible if someone gets creative)

Something like this:

Suggested change

	let atime_secs = this.0.atime();
	system_time_to_lua_time(lua, Some(atime_secs))
	let secs = this.0.atime();
	let nsec = this.0.atime_nsec();
	let dt = DateTime::<Utc>::from_timestamp(secs, nsec)
	.map_err(mlua::Error::external)?;
	Ok(Time::from(dt))

which you can also turn into a little macro for the 3 different timestamps or amend the system_time_to_lua_time helper function accordingly.

[wez]

I'd appreciate having a separate doc page for symlink_metadata_for_path to make the search experience (potentially!) better, but it needn't copy the full text from here; it can have a stub paragraph below its synopsis and other metadata that says something like:

This function behaves exactly like [metadata_for_path](metadata_for_path.md),
except that it does not follow symbolic links and instead returns information
about the symbolic link itself.

[wez]

Thank you!