Add kem support #1976

Job	Run time
basic_clang	4m 57s
basic_gcc	4m 50s
check_docs	46s
check_update	1m 12s
check-ansi	2m 38s
minimal	2m 22s
no-deprecated	4m 32s
non-caching	13m 34s
no-shared-macos	6m 59s
no-shared-ubuntu	3m 46s
self-hosted (freebsd-13.2)	1s
self-hosted (ubuntu-arm64-22.04)	1s
address_ub_sanitizer	10m 2s
enable_non-default_options	3m 56s
external-test-pyca (1.51.0, 3.9)	7m 32s
external-tests	10m 57s
external-test-cf-quiche	3m 43s
full_featured	5m 23s
fuzz_tests	2m 56s
legacy	3m 57s
memory_sanitizer	19m 47s
no-legacy	4m 54s
out-of-readonly-source-and-install-macos	17m 58s
out-of-readonly-source-and-install-ubuntu	6m 35s
threads_sanitizer	6m 14s
	2h 29m 32s

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