refactor(pkg): speed up opam file parsing (#11435) #29893

Job	Run time
Nix (macos-latest)	1m 59s
Build (macos-latest, 5.1.x)	1m 2s
Nix (ubuntu-latest)	57s
Documentation	52s
Build (ubuntu-latest, 5.1.x)	8m 39s
Build (ocaml-variants.5.4.0+trunk, ubuntu-latest, true)	1m 25s
Build (4.14.x, ubuntu-latest, true)	1m 30s
Format	1m 2s
Coq 8.16.1	7m 4s
Build (4.14.x, macos-latest, true)	51s
Build (5.1.x, macos-13, true)	3m 44s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	14m 24s
Wasm_of_ocaml	10m 14s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 7s
Build (4.08.x, ubuntu-latest, true)	1m 31s
Build (4.04.x, ubuntu-latest, true, true)	4m 33s
Build (4.02.x, ubuntu-latest, true)	1m 3s
Build microbenchmarks	2m 32s
Create local opam switch (macos-latest, 5)	1s
Create local opam switch (macos-latest, 4.14)	44s
Build monorepo benchmark docker image	4m 4s
Create local opam switch (ubuntu-latest, 5)	45s
Create local opam switch (ubuntu-latest, 4.14)	44s
	1h 17m 47s

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