fix: init hidden state for reactant #3686

Job	Run time
downgrade	1h 9m 10s
test (1.10, ubuntu-latest, core_layers)	16m 18s
test (1.10, ubuntu-latest, normalize_layers)	14m 5s
test (1.10, ubuntu-latest, recurrent_layers)	19m 30s
test (1.10, ubuntu-latest, autodiff)	23m 51s
test (1.10, ubuntu-latest, misc)	29m 27s
test (1.10, ubuntu-latest, reactant)	11m 36s
test (1, ubuntu-latest, core_layers)	18m 42s
test (1, ubuntu-latest, normalize_layers)	16m 31s
test (1, ubuntu-latest, recurrent_layers)	22m 18s
test (1, ubuntu-latest, autodiff)	24m 32s
test (1, ubuntu-latest, misc)	31m 39s
test (1, ubuntu-latest, reactant)	15m 43s
test (1.10, macos-latest, all)	3h 42m 9s
test (1.10, windows-latest, all)	1h 16m 35s
	10h 12m 6s

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