Tests

Replace SeedableRng impl for SmallRng with inherent fns #632

Job	Run time
Check doc	1m 6s
test-ios	2m 3s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	1m 1s
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	1m 32s
test-miri	3m 1s
test-no-std	12s
test (macos-latest, x86_64-apple-darwin, stable)	2m 34s
test (windows-latest, x86_64-pc-windows-gnu, stable)	1m 43s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 48s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	2m 26s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	1m 50s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	1m 24s
	20m 40s

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