refactor: cleanups in the opam solver #29903

Job	Run time
Format	1m 3s
Documentation	59s
Build (macos-latest, 5.1.x)	45s
Nix (macos-latest)	2m 10s
Build (ubuntu-latest, 5.1.x)	8m 32s
Build microbenchmarks	2m 29s
Coq 8.16.1	6m 49s
Build (ocaml-variants.5.4.0+trunk, ubuntu-latest, true)	1m 31s
Nix (ubuntu-latest)	52s
Build (4.14.x, ubuntu-latest, true)	2m 28s
Build (4.14.x, macos-latest, true)	1m 1s
Create local opam switch (macos-latest, 5)	35s
Build (5.1.x, macos-13, true)	4m 35s
Build monorepo benchmark docker image	2m 49s
Create local opam switch (macos-latest, 4.14)	49s
Wasm_of_ocaml	9m 45s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	13m 57s
Create local opam switch (ubuntu-latest, 5)	1m 22s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 11s
Create local opam switch (ubuntu-latest, 4.14)	1m 35s
Build (4.08.x, ubuntu-latest, true)	1m 26s
Build (4.04.x, ubuntu-latest, true, true)	4m 25s
Build (4.02.x, ubuntu-latest, true)	2m 42s
	1h 20m 50s

Provide feedback