Tests

Add WeightedIndexTree to rand_distr #638

Job	Run time
test-ios	31s
Check doc	1m 6s
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	1m 18s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	54s
test-miri	2m 13s
test (macos-latest, x86_64-apple-darwin, stable)	1m 57s
test (windows-latest, x86_64-pc-windows-gnu, stable)	3m 11s
test-no-std	12s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 59s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	2m 59s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	1m 33s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	1m 5s
	18m 58s

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