📝 Add design thoughts for `bitset` #1069

Job	Run time
quality_checks_pass	1m 5s
mutate	1m 5s
sanitize (undefined, gcc)	1m 5s
sanitize (thread, gcc)	1m 5s
valgrind	1m 5s
sanitize (address, gcc)	1m 5s
sanitize (undefined, clang)	1m 5s
sanitize (address, clang)	1m 5s
sanitize (thread, clang)	1m 5s
build_and_test_24 (clang, 18, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (clang, 19, 23, libc++, Debug)	1m 5s
build_and_test_24 (clang, 21, 23, libc++, Debug)	1m 5s
build_and_test_24 (clang, 20, 23, libc++, Debug)	1m 5s
build_and_test_24 (clang, 20, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (clang, 21, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (clang, 18, 23, libc++, Debug)	1m 5s
build_and_test_24 (gcc, 13, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (clang, 22, 23, libc++, Debug)	1m 5s
build_and_test_24 (clang, 19, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (gcc, 14, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (clang, 22, 23, libstdc++, Debug)	1m 5s
build_and_test_24 (gcc, 12, 23, libstdc++, Debug)	1m 5s
merge_ok	1s
	23m 51s

Provide feedback