Add additional EVP_SKEY helpers #620

Job	Run time
address_ub_sanitizer	10m 55s
basic_clang	6m 13s
basic_gcc	5m 59s
check_docs	58s
check_update	1m 23s
check-ansi	2m 47s
enable_non-default_options	4m 50s
freebsd-x86_64	7m 42s
full_featured	6m 48s
fuzz_tests	3m 0s
legacy	4m 42s
linux-arm64	1s
memory_sanitizer	16m 27s
minimal	2m 46s
no-deprecated	5m 36s
no-legacy	5m 51s
non-caching	14m 18s
no-shared-macos (macos-13)	12m 26s
no-shared-macos (macos-14)	4m 52s
no-shared-ubuntu	4m 43s
out-of-readonly-source-and-install-ubuntu	7m 45s
threads_sanitizer	5m 4s
external-tests-misc	8m 12s
external-tests-providers	9m 50s
external-tests-pyca (1.51.0, 3.9)	6m 59s
out-of-readonly-source-and-install-macos (macos-13)	15m 43s
out-of-readonly-source-and-install-macos (macos-14)	8m 0s
	3h 3m 50s

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