refactor(@angular/build): provide karma runner for unit-test builder #7749

Job	Run time
build	2m 45s
lint	2m 6s
e2e_windows (windows-2025, 22, npm, 3)	2m 31s
e2e_windows (windows-2025, 22, npm, 1)	19s
e2e_windows (windows-2025, 22, esbuild, 1)	20s
e2e_windows (windows-2025, 22, npm, 2)	2m 31s
e2e_windows (windows-2025, 22, npm, 5)	2m 31s
e2e_windows (windows-2025, 22, esbuild, 5)	2m 31s
e2e_windows (windows-2025, 22, npm, 0)	19s
e2e_windows (windows-2025, 22, esbuild, 4)	2m 31s
e2e_windows (windows-2025, 22, esbuild, 0)	2m 32s
e2e_windows (windows-2025, 22, esbuild, 2)	20s
e2e_windows (windows-2025, 22, esbuild, 3)	2m 29s
e2e_windows (windows-2025, 22, npm, 4)	2m 32s
Browser Compatibility Tests	1s
e2e-package-managers	1s
e2e-snapshots	1s
test	1s
publish-snapshots	1s
e2e	1s
	26m 23s

Provide feedback