GH-125413: Add private metadata methods topathlib.Path.info#129897

Add the following private methods to `pathlib.Path.info`:- `_get_mode()`: returns the POSIX file mode (`st_mode`), or zero if  `os.stat()` fails.- `_get_times_ns()`: returns the access and modify times in nanoseconds  (`st_atime_ns` and `st_mtime_ns`), or zeroes if `os.stat()` fails.- `_get_flags()`: returns the BSD file flags (`st_flags`), or zero if  `os.stat()` fails.- `_get_xattrs()`: returns the file extended attributes as a list of  key, value pairs, or an empty list if `listxattr()` or `getattr()` fail.These methods replace `LocalCopyReader.read_metadata()`, and so we candelete the `CopyReader` and `LocalCopyReader` classes. Rather than readingmetadata via `source._copy_reader.read_metadata()`, we instead call`source.info._get_mode()`, `_get_times_ns()`, etc.Copying metadata is only supported for local-to-local copies at the moment.To support copying between arbitrary `ReadablePath` and `WritablePath`objects, we'd need to make the new methods public and documented.