Clear out unsound overflows/underflows

[LesnyRumcajs]

Summary

With the current profile we're building with, Forest will panic (and then abort) on overflow/underflow. I'm inclined to keep it for now for correctness purposes. (better fail fast rather than continue with some garbage data).

We need some safeguards, especially where users or peers are providing input.

Completion Criteria

• Iterate over possible places where a user-supplied underflow/overflow might happen
• harden those
• there might be cases where the logic was blindly copied from Lotus which would do likely wrapping overflows. In case such thing is not sound, this must be reported to FilOz as well.

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