Cleaned up tests by bringing objects under `mini_core` into scope #2529

Job	Run time
build_system	25s
duplicates	3s
build (gcc-15.deb, --std-tests)	2m 59s
build (gcc-15.deb, --test-libcore)	3m 0s
build (gcc-15.deb, --extended-rand-tests)	4m 37s
build (gcc-15.deb, --extended-regex-example-tests)	3m 15s
build (gcc-15.deb, --extended-regex-tests)	3m 52s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	3m 38s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	3m 0s
build (gcc-15.deb, --projects)	3m 18s
build (gcc-15-without-int128.deb, --std-tests)	3m 0s
build (gcc-15-without-int128.deb, --test-libcore)	3m 1s
build (gcc-15-without-int128.deb, --extended-rand-tests)	3m 14s
build (gcc-15-without-int128.deb, --extended-regex-example-tests)	3m 10s
build (gcc-15-without-int128.deb, --extended-regex-tests)	3m 11s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	3m 4s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	3m 0s
build (gcc-15-without-int128.deb, --projects)	2m 59s
success	1s
	52m 47s

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