refactor(pkg): switch to Stdune maps #29576

Job	Run time
Format	1m 5s
Nix (macos-latest)	2m 16s
Nix (ubuntu-latest)	52s
Coq 8.16.1	7m 5s
Build (macos-latest, 5.1.x)	1s
Documentation	56s
Build (ubuntu-latest, 5.1.x)	8m 25s
Wasm_of_ocaml	8m 27s
Build (ocaml-variants.5.4.0+trunk, ubuntu-latest, true)	1m 31s
Build microbenchmarks	2m 33s
Build (4.14.x, ubuntu-latest, true)	1m 28s
Build (4.14.x, macos-latest, true)	1m 58s
Create local opam switch (macos-latest, 5)	3m 22s
Build monorepo benchmark docker image	3m 42s
Build (5.1.x, macos-13, true)	2m 19s
Create local opam switch (macos-latest, 4.14)	4m 31s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	8m 20s
Create local opam switch (ubuntu-latest, 5)	4m 50s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 18s
Create local opam switch (ubuntu-latest, 4.14)	4m 54s
Build (4.08.x, ubuntu-latest, true)	1m 31s
Build (4.04.x, ubuntu-latest, true, true)	4m 29s
Build (4.02.x, ubuntu-latest, true)	3m 48s
	1h 26m 41s

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