Factor out source.dump/source.drop #11748

Job	Run time
build_details	2s
build_opam (4.14.x)	8m 51s
build_js	1m 55s
build_opam (5.2.x)	5m 24s
lezer_parse	52s
run_tests (@citest)	13m 14s
build_posix (debian_trixie, amd64)	14m 2s
tree_sitter_parse	49s
run_tests (@doctest)	7m 47s
build_posix (debian_bookworm, amd64)	14m 18s
run_tests (@mediatest)	12m 26s
build_no_depopts	6m 4s
update_doc	0s
build_posix (ubuntu_oracular, amd64)	14m 33s
build_win32 (x64)	17m 46s
build_posix (ubuntu_noble, amd64)	14m 17s
build_posix (alpine, amd64)	11m 36s
fetch_s3_artifacts	20s
build_docker_alpine (amd64)	52s
build_docker (amd64)	3m 3s
build_docker_minimal (amd64)	2m 52s
build_docker_alpine_minimal (amd64)	1m 3s
update_release	0s
build_docker_release-minimal	0s
build_docker_release	0s
	2h 32m 6s

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