v0.9.1

Added

• symlink_to(..., force=True) — replace an existing entry at the link
  path instead of failing. SFTP has no atomic "replace symlink", so every
  consumer was re-implementing the unlink-then-symlink dance. Implemented at
  the Path layer over a new _symlink_to() backend primitive (the same
  wrapper/primitive split as _mkdir/mkdir), so all backends inherit it.
  Removes a non-directory entry only, and is documented as non-atomic.
• chown(uid=None, gid=None) over a new _chown() backend primitive.
  chown was the one POSIX permission attribute stat() could read but
  nothing could write back. None means "leave unchanged"; the normalization
  lives on Path so each backend receives an already-canonical pair rather
  than re-deriving the mapping (os.chown wants -1, SFTP omits the field).
• chmod() accepts a string octal mode ("0755"), normalized with an
  explicit base-8 parse. A mode string outside [0-7] raises rather than
  being coerced — int("0755") in decimal is a different mode, which is
  exactly the wrong-but-plausible failure this guards.

Changed

• Adopted black, pinned to the 3.9 floor; src/ and tests/ reformatted.

Full Changelog: v0.9.0...v0.9.1