test: organize stanza tests better #28883

Job	Run time
Nix (macos-latest)	1m 56s
Coq 8.16.1	7m 7s
Coverage (5.1.x)	9m 44s
Nix (ubuntu-latest)	55s
Build (macos-latest, 5.1.x)	16m 27s
Documentation	52s
Format	1m 5s
Build (ubuntu-latest, 5.1.x)	8m 48s
Build monorepo benchmark docker image	1m 40s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	5m 11s
Build microbenchmarks	2m 18s
Build (4.14.x, ubuntu-latest, true)	1m 34s
Create local opam switch (macos-latest, 5)	5m 36s
Build (4.14.x, macos-latest, true)	2m 24s
Build (5.1.x, macos-13, true)	4m 45s
Create local opam switch (macos-latest, 4.14)	5m 38s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	16m 0s
Create local opam switch (ubuntu-latest, 5)	5m 6s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	10m 27s
Create local opam switch (ubuntu-latest, 4.14)	5m 21s
Build (4.08.x, ubuntu-latest, true)	1m 48s
Build (4.04.x, ubuntu-latest, true, true)	4m 45s
Build (4.02.x, ubuntu-latest, true)	4m 8s
	2h 3m 35s

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