feat: update ConvMixer to support reactant #3926

Job	Run time
downgrade	5m 5s
test (1.10, ubuntu-latest, core_layers)	19m 36s
test (1.10, ubuntu-latest, normalize_layers)	19m 47s
test (1.10, ubuntu-latest, recurrent_layers)	28m 16s
test (1.10, ubuntu-latest, autodiff)	31m 53s
test (1.10, ubuntu-latest, misc)	28m 54s
test (1.10, ubuntu-latest, reactant)	7m 40s
test (1, ubuntu-latest, core_layers)	23m 51s
test (1, ubuntu-latest, normalize_layers)	22m 2s
test (1, ubuntu-latest, recurrent_layers)	12m 2s
test (1, ubuntu-latest, autodiff)	26m 39s
test (1, ubuntu-latest, misc)	22m 5s
test (1, ubuntu-latest, reactant)	8m 45s
test (1, macos-latest, all)	31m 54s
test (1, windows-latest, all)	31m 38s
	5h 20m 7s

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