Add semi-additive categories infrastructure #3910

Job	Run time
opam-build (latest, ubuntu-latest)	4m 40s
build (latest)	3m 35s
opam-build (dev, ubuntu-latest)	4m 16s
opam-build (supported, ubuntu-latest)	4m 39s
build (supported)	4m 11s
quick-build (latest, ubuntu-latest)	3m 45s
nix	2m 10s
quick-build (dev, ubuntu-latest)	3m 21s
build (dev, --warnings)	3m 55s
quick-build (supported, ubuntu-latest)	3m 48s
doc-alectryon	4m 55s
doc-coqdoc	1m 52s
doc-timing	1m 47s
doc-dep-graphs	4m 57s
install (supported)	2m 3s
coqchk (latest)	2m 20s
install (dev)	1m 49s
coqchk (supported)	2m 18s
install (latest)	1m 43s
coqchk (dev)	2m 3s
delete-artifacts	10s
deploy-doc	1s
	1h 4m 18s

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