Support SM2 two-party threshold signature #14

Job	Run time
basic_clang	4m 17s
basic_gcc	4m 22s
check_update	56s
check-ansi	1m 54s
minimal	2m 5s
address_ub_sanitizer	11m 5s
buildtest	6m 46s
enable_non-default_options	3m 37s
fips_and_ktls	4m 16s
legacy	3m 41s
memory_sanitizer	26m 9s
no-deprecated	3m 52s
no-legacy	4m 16s
non-caching	4m 21s
no-shared (ubuntu-latest)	3m 10s
no-shared (macos-latest)	4m 23s
ntls_address_ub_sanitizer	9m 51s
ntls_memory_sanitizer	17m 44s
symbol_prefix-test	7m 7s
threads_sanitizer	3m 30s
EC_POINTs_api_test	18m 45s
external-test-pyca (1.51.0, 3.9)	1m 24s
ntls-with-fips	7m 45s
ntls-without-sm234	6m 39s
out-of-source-and-install (ubuntu-latest)	4m 18s
phe_test	36m 7s
out-of-source-and-install (macos-latest)	6m 33s
sm2-threshold-test	44m 26s
smtc_and_ntls	14m 30s
zkp-build-test	3m 19s
	4h 31m 8s

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