Remove usage of legacy build system from build tests (#8179) #9288

Job	Run time
build-compiler (windows-2025, 5.3.0, true, win32-x64, x86_64-pc-windows-gnu, .exe)	6m 23s
build-compiler (macos-15, 5.3.0, true, darwin-arm64, aarch64-apple-darwin)	5m 12s
build-compiler (ubuntu-24.04, ocaml-variants.5.0.0+options,ocaml-option-static, linux-x64, x86_64...	2m 35s
build-compiler (macos-15-intel, 5.3.0, true, darwin-x64, x86_64-apple-darwin)	7m 14s
build-compiler (ubuntu-24.04, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, linux...	3m 10s
build-compiler (ubuntu-24.04-arm, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, t...	4m 29s
pkg-pr-new	57s
api-docs	1m 38s
test-integration-rewatch (macos-15-intel)	4m 2s
test-installation-npm (macos-15-intel)	30s
test-integration-rewatch (ubuntu-24.04-arm)	1m 12s
test-installation-pnpm (ubuntu-24.04)	12s
test-installation-npm (windows-2025)	1m 1s
test-installation-npm (ubuntu-24.04-arm)	21s
test-integration-rewatch (ubuntu-24.04)	1m 18s
test-installation-pnpm (windows-2025)	34s
test-installation-pnpm (macos-15)	21s
test-integration-rewatch (windows-2025)	2m 52s
test-installation-npm (macos-15)	20s
test-installation-npm (ubuntu-24.04)	14s
test-installation-pnpm (ubuntu-24.04-arm)	18s
test-installation-pnpm (macos-15-intel)	32s
test-integration-rewatch (macos-15)	2m 27s
publish	0s
	47m 52s

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