GH-125413: Add private metadata methods to pathlib.Path.info (#129897)

Add the following private methods to `pathlib.Path.info`:

- `_posix_permissions()`: the POSIX file permissions (`S_IMODE(st_mode)`)
- `_file_id()`: the file ID (`(st_dev, st_ino)`)
- `_access_time_ns()`: the access time in nanoseconds (`st_atime_ns`)
- `_mod_time_ns()`: the modify time in nanoseconds (`st_mtime_ns`)
- `_bsd_flags()`: the BSD file flags (`st_flags`)
- `_xattrs()`: the file extended attributes as a list of key, value pairs,
  or an empty list if `listxattr()` or `getxattr()` fail in an ignorable 
  way.

These methods replace `LocalCopyReader.read_metadata()`, and so we can
delete the `CopyReader` and `LocalCopyReader` classes. Rather than reading
metadata via `source._copy_reader.read_metadata()`, we instead call
`source.info._posix_permissions()`, `_access_time_ns()`, etc.

Preserving metadata is only supported for local-to-local copies at the
moment. To support copying metadata between arbitrary `ReadablePath` and
`WritablePath` objects, we'd need to make the new methods public and
documented.

Co-authored-by: Petr Viktorin <encukou@gmail.com>

Lib/pathlib/_local.py

@@ -19,7 +19,7 @@ try:
 except ImportError:
     grp = None
 
-from pathlib._os import LocalCopyReader, LocalCopyWriter, PathInfo, DirEntryInfo
+from pathlib._os import LocalCopyWriter, PathInfo, DirEntryInfo, ensure_different_files
 
 
 __all__ = [
@@ -1079,7 +1079,6 @@ class Path(PurePath):
         os.replace(self, target)
         return self.with_segments(target)
 
-    _copy_reader = property(LocalCopyReader)
     _copy_writer = property(LocalCopyWriter)
 
     def copy(self, target, follow_symlinks=True, dirs_exist_ok=False,
@@ -1125,7 +1124,7 @@ class Path(PurePath):
         else:
             if not hasattr(target, '_copy_writer'):
                 target = self.with_segments(target_str)
-            target._copy_writer._ensure_different_file(self)
+            ensure_different_files(self, target)
             try:
                 os.replace(self, target_str)
                 return target