Feature request: add hardsilu / hardswish activation

Feature request: add hardsilu / hardswish activation: a task in MiMo-V2.6-RL-harbor-code: MiMo-V2.6-RL Code (Harbor) (Harbor dataset). I was looking through ivy 's experimental activations and noticed quite a lot of them are already there — silu , relu6 , hardtanh , hardshrink , selu , elu , celu…

The task

I was looking through `ivy`'s experimental activations and noticed quite a lot of them are already there — `silu`, `relu6`, `hardtanh`, `hardshrink`, `selu`, `elu`, `celu`, etc. — but I couldn't find `hardsilu` (a.k.a. `hardswish`).

Part of FineEnvs/MiMo-V2.6-RL-harbor-code.