Tests

Add WeightedIndexTree to rand_distr #640

Job	Run time
test-miri	2m 21s
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	52s
Check doc	1m 7s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	38s
test (macos-latest, x86_64-apple-darwin, stable)	1m 38s
test-ios	32s
test-no-std	12s
test (windows-latest, x86_64-pc-windows-gnu, stable)	3m 1s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 55s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	2m 31s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	1m 32s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	1m 3s
	17m 22s

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