Obtain the time at which the file or directory was last modified.
The operation may fail with:
- isPermissionError if the user is not permitted to read
the modification time; or
- isDoesNotExistError if the file or directory does not
exist.
Caveat for POSIX systems: This function returns a timestamp with
sub-second resolution only if this package is compiled against
unix-2.6.0.0 or later and the underlying filesystem supports
them.