miscellaneous cleanups
Per Rob's comment https://discord.com/channels/435943710472011776/813919248455827515/1539144885255536761 and in the spirit of similar PRs.
Feel free to comment whatever uncontroversial claenups and I will apply them
Changes:
- Add Jonathan to `AUTHORS` which we missed when merging pawn-pair inputs
- Mr. Dubslow's changes from https://github.com/official-stockfish/Stockfish/pull/6942
- mstembera's style tweaks
- niklasf's CLOEXEC enjoyment
- lemtea's `.size() == 0` -> `empty()`
closes https://github.com/official-stockfish/Stockfish/pull/7074
No functional change
Co-authored-by: Dubslow <bunslow@gmail.com>