Add support for bigstring. #9549

Job	Run time
pre-commit	2m 47s
build_details	3s
build_js	1m 22s
build_no_depopts	3m 38s
tree_sitter_parse	56s
build_opam (4.14.x)	3m 47s
build_posix (debian_trixie, amd64)	3m 36s
build_opam (5.0.x)	3m 46s
build_posix (debian_bookworm, amd64)	3m 40s
build_win32 (x64)	3m 38s
build_posix (ubuntu_jammy, amd64)	3m 38s
build_posix (ubuntu_lunar, amd64)	3m 36s
lezer_parse	50s
build_posix (alpine, amd64)	3m 38s
run_tests (@citest)	3m 29s
run_tests (@doctest)	7s
update_doc	0s
run_tests (@mediatest)	3m 24s
fetch_s3_artifacts	1s
build_docker_alpine	1s
build_docker	1s
update_release	1s
build_docker_minimal	1s
build_docker_alpine_minimal	1s
build_docker_release	1s
build_docker_release-minimal	1s
	46m 3s

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