✨ Add `into_variant` #376

Job	Run time
quality_checks_pass	1m 10s
build_and_test_24 (clang, 16, 20, libstdc++, Debug)	3m 29s
sanitize (undefined, clang)	3m 28s
build_and_test_24 (clang, 16, 20, libc++, Debug)	3m 27s
build_and_test_22 (clang, 14, 20, libc++, Debug)	3m 2s
sanitize (undefined, gcc)	4m 34s
valgrind	8m 11s
build_and_test_24 (clang, 17, 20, libstdc++, Debug)	3m 16s
build_and_test_22 (clang, 15, 20, libstdc++, Debug)	2m 51s
sanitize (address, clang)	3m 24s
build_and_test_24 (clang, 17, 20, libc++, Debug)	3m 42s
build_and_test_22 (clang, 15, 20, libc++, Debug)	3m 40s
sanitize (address, gcc)	4m 0s
build_and_test_24 (clang, 18, 20, libstdc++, Debug)	3m 21s
sanitize (thread, clang)	3m 30s
build_and_test_24 (clang, 18, 20, libc++, Debug)	4m 20s
sanitize (thread, gcc)	3m 45s
build_and_test_24 (gcc, 12, 20, libstdc++, Debug)	3m 45s
build_and_test_24 (gcc, 13, 20, libstdc++, Debug)	3m 31s
merge_ok	7s
	1h 10m 33s

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