Changes:
* Drop support for Python 3.7, which has reached its end of life.
* ``chess.engine.EventLoopPolicy`` is no longer needed and now merely an alias
for the default event loop policy.
* If available and requested via ``setpgrp``, use ``process_group`` support
from Python 3.11 for engine processes.
* No longer eagerly reject 8 piece positions in ``chess.syzygy``, so that
some 8 piece positions with decisive captures can be probed successfully.
* The string wrapper returned by ``chess.svg`` functions now also implements
``_repr_html_``.
* Significant changes to ``chess.engine`` internals:
``chess.engine.BaseCommand`` methods other than the constructor no longer
receive ``engine: Protocol``.
* Significant changes to board state internals: Subclasses of ``chess.Board``
can no longer hook into board state recording/restoration and need to
override relevant methods instead (``clear_stack``, ``copy``, ``root``,
``push``, ``pop``).
New features:
* Add ``chess.pgn.Game.time_control()`` and related data models.
* Add model ``sf16.1`` for ``chess.engine.Score.wdl()``, the new default.
Bugfixes:
* Fix unsolicited engine output may cause assertion errors with regard to
command states.
* Fix handling of whitespace in UCI engine communication.
* For ``chess.Board.epd()`` and ``chess.Board.set_epd()``, require that EPD
opcodes start with a letter.
