v0.21.0

Changes

• Add cleanup_socket param on create_unix_server()
  (#623) (by @fantix in d6114d2)

Fixes

• Use cythonized SO_REUSEPORT rather than the unwrapped native one. (#609)
  (by @ptribble in 4083a94 for #550)

• UDP errors should result in protocol.error_received (#601)
  (by @jensbjorgensen in 3c3bbef)

• Updates for Cython3 (#587)
  (by @alan-brooks in 3fba9fa for #587)

• Test with Python 3.13 (#610)
  (by @edgarrmondragon in fb5a139)