Add batching for TSS signatures when aggregating in prehandle

For the main case of multiple valid partial signatures, it is more efficient to do a batch verification of those signatures.

This is straightforward to take advantage of when aggregating partial signatures in pre-handle, since in that case a node does not need be _certain_ any particular signature is validated before its `TssPartialSignature` reaches consensus, and can instead lazily collect signatures for a batch large enough to cross the signing threshold.