feat: add `act_fn` param to `OutValueFunctionBlock` (#3994)
* feat: add act_fn param to OutValueFunctionBlock
* feat: update unet1d tests to not use mish
* feat: add `mish` as the default activation function
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
* feat: drop mish tests from unet1d
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Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
