Add comparison operators for `CodingKey` #18

Job	Run time
Linux (Debian) (armv7, 6.1.2, debug, debian, bullseye)	2m 11s
Linux (Debian) (armv7, 6.1.2, release, debian, bookworm)	7m 12s
Linux (Raspios) (armv6, 6.1.2, release, raspios, bookworm)	6m 48s
Linux (Raspios) (armv7, 6.1.2, debug, raspios, bookworm)	2m 4s
Linux (Raspios) (armv6, 6.1.2, debug, raspios, bookworm)	2m 18s
Linux (Debian) (armv7, 6.1.2, release, debian, bullseye)	6m 57s
Linux (Debian) (armv7, 6.1.2, debug, debian, bookworm)	2m 7s
Linux (Raspios) (armv7, 6.1.2, release, raspios, bookworm)	6m 45s
	36m 22s

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