refactor(@angular/build): optimize vitest in-memory file loading #2490

Job	Run time
list	22s
workflow (modules-builder-tests)	1m 50s
workflow (build-cli)	1m 40s
workflow (devkit-core-tests)	1m 15s
workflow (devkit-core-tests-rerun)	1m 17s
workflow (build-unit-tests)	2m 20s
	8m 44s

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