chore: bump madsim to 0.2.31 #922

Job	Run time
check	2m 27s
doc	1m 7s
bench	2m 6s
build	3m 9s
test-sim (ubuntu-latest, stable)	3m 53s
test-std (ubuntu-latest, stable)	3m 51s
test-sim (ubuntu-latest, nightly)	4m 2s
test-std (ubuntu-latest, nightly)	3m 57s
test-sim (macos-latest, stable)	3m 19s
test-std (macos-latest, stable)	3m 12s
test-sim (macos-latest, nightly)	3m 36s
test-std (macos-latest, nightly)	3m 15s
	37m 54s

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