refactor(pkg): use stdune more consistently in solver #29437

Job	Run time
Documentation	55s
Build (macos-latest, 5.1.x)	13m 1s
Build (ubuntu-latest, 5.1.x)	8m 25s
Format	1m 6s
Coq 8.16.1	7m 7s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	1m 43s
Build monorepo benchmark docker image	3m 36s
Build (4.14.x, ubuntu-latest, true)	1m 32s
Build (4.14.x, macos-latest, true)	2m 13s
Nix (macos-latest)	2m 3s
Build (5.1.x, macos-13, true)	4m 13s
Build microbenchmarks	2m 26s
Nix (ubuntu-latest)	52s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	14m 50s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 14s
Build (4.08.x, ubuntu-latest, true)	1m 34s
Wasm_of_ocaml	10m 49s
Build (4.04.x, ubuntu-latest, true, true)	4m 30s
Create local opam switch (macos-latest, 5)	5m 48s
Build (4.02.x, ubuntu-latest, true)	3m 54s
Create local opam switch (macos-latest, 4.14)	6m 29s
Create local opam switch (ubuntu-latest, 5)	4m 54s
Create local opam switch (ubuntu-latest, 4.14)	4m 56s
	1h 55m 10s

Provide feedback