[design] Make it possible to use explicitly fetched signature impleme… #955

Job	Run time
compiler (gcc-7, ubuntu-20.04)	9m 7s
compiler (gcc-8, ubuntu-20.04)	10m 7s
compiler (gcc-9, ubuntu-20.04)	9m 11s
compiler (gcc-10, ubuntu-20.04)	7m 58s
compiler (gcc-11, ubuntu-22.04)	9m 2s
compiler (gcc-12, ubuntu-22.04)	8m 50s
compiler (gcc-13, ubuntu-22.04, ubuntu-toolchain-r/test)	10m 12s
compiler (clang-6.0, ubuntu-20.04)	8m 13s
compiler (clang-7, ubuntu-20.04)	7m 47s
compiler (clang-8, ubuntu-20.04)	10m 59s
compiler (clang-9, ubuntu-20.04)	10m 36s
compiler (clang-10, ubuntu-20.04)	8m 14s
compiler (clang-11, ubuntu-20.04)	8m 20s
compiler (clang-12, ubuntu-20.04)	7m 41s
compiler (clang-13, ubuntu-22.04)	8m 1s
compiler (clang-14, ubuntu-22.04)	7m 51s
compiler (clang-15, ubuntu-22.04, jammy)	10m 19s
compiler (clang-16, ubuntu-22.04, jammy)	8m 37s
	2h 41m 5s

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