Implement Forest Slasher 🪓

# Summary

Implementing Forest's version of a slasher should be relatively straightforward, possibly making lightweight Forest nodes actually earn some FIL.

We already have consensus fault verification logic in Forest (even duplicated in a few places...). We are missing a mechanism to react to consensus fault errors (it could be an optional service in the same monolith like in Lotus) that submits consensus fault reports.

# Completion Criteria

- [ ] The slasher is implemented and disabled by default, given that it might generate gas fees without any rewards.
- [ ] Good test coverage for this might be tricky, but there should be proof that it works (successful slash on https://calibration.filfox.info/en/message?)
- [ ] the slasher is configurable (it might have a separate section in the config if needed)
- [ ] user-facing docs are in place

# Additional Links & Resources

https://lotus.filecoin.io/lotus/manage/slasher-and-disputer/
https://github.com/filecoin-project/lotus/blob/master/chain/gen/slashfilter/slashsvc/slashservice.go
https://github.com/filecoin-project/lotus/blob/614868b1d42722dbbbdd5ac7eaed423e88af62ef/node/config/types.go#L668-L686