Tests

Replace SeedableRng impl for SmallRng with inherent fns #631

Job	Run time
test-miri	3m 5s
Check doc	1m 9s
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	1m 36s
test-ios	26s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	59s
test-no-std	13s
test (macos-latest, x86_64-apple-darwin, stable)	4m 12s
test (windows-latest, x86_64-pc-windows-gnu, stable)	1m 57s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 40s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	2m 24s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	47s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	44s
	19m 12s

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