Create an alert or avenue to run code if a recipient responded with incorrect proof

[sarahsturgeon]

Right now, if the recipient sends back an incorrect proof, it would be a no-op because the callback wouldn't be found in the awaitingProof table (ref: https://github.com/CFC-Servers/gm_express/blob/main/lua/gm_express/sh_init.lua#L131-L141)

We should have some way of erroring or alerting of this case at minimum, but letting the sender define an error handling function would also be nice.