Implement `from_seed_unchecked` for `Ed25519KeyPair` #151

Job	Run time
GCC 4.8 - CMake 0 - FIPS 0	6m 24s
GCC 4.8 - CMake 0 - FIPS 1	8m 19s
GCC 5 - CMake 0 - FIPS 0	6m 28s
GCC 7 - CMake 0 - FIPS 0	4m 0s
GCC 5 - CMake 0 - FIPS 1	7m 46s
GCC 7 - CMake 0 - FIPS 1	5m 22s
GCC 6 - CMake 0 - FIPS 0	6m 33s
GCC 8 - CMake 0 - FIPS 0	4m 8s
GCC 6 - CMake 0 - FIPS 1	7m 41s
GCC 8 - CMake 0 - FIPS 1	5m 18s
GCC 4.8 - CMake 1 - FIPS 0	6m 30s
GCC 7 - CMake 1 - FIPS 0	4m 3s
GCC 4.8 - CMake 1 - FIPS 1	8m 0s
GCC 5 - CMake 1 - FIPS 0	6m 39s
C-std ubuntu-latest - 11 - Force CMake 0	1m 49s
GCC 7 - CMake 1 - FIPS 1	5m 35s
GCC 5 - CMake 1 - FIPS 1	7m 35s
GCC 8 - CMake 1 - FIPS 0	3m 46s
C-std ubuntu-latest - 11 - Force CMake 1	1m 52s
GCC 6 - CMake 1 - FIPS 0	6m 32s
GCC 8 - CMake 1 - FIPS 1	5m 35s
C-std ubuntu-latest - 99 - Force CMake 0	1m 45s
GCC 6 - CMake 1 - FIPS 1	8m 42s
C-std ubuntu-latest - 99 - Force CMake 1	2m 14s
C-std macos-13 - 11 - Force CMake 0	2m 36s
C-std macos-13 - 11 - Force CMake 1	2m 9s
C-std macos-13 - 99 - Force CMake 0	2m 41s
C-std macos-13 - 99 - Force CMake 1	2m 37s
C-std macos-14-xlarge - 11 - Force CMake 0	1m 18s
C-std macos-14-xlarge - 11 - Force CMake 1	1m 29s
C-std macos-14-xlarge - 99 - Force CMake 0	1m 32s
C-std macos-14-xlarge - 99 - Force CMake 1	1m 22s
C-std windows-latest - 11 - Force CMake 0	4m 37s
C-std windows-latest - 11 - Force CMake 1	5m 23s
C-std windows-latest - 99 - Force CMake 0	3m 31s
C-std windows-latest - 99 - Force CMake 1	4m 47s
	2h 46m 38s

Provide feedback