Add way to pass full transaction context

[benthecarman]

Currently when you pass in a script and witness, tapsim will generate a dummy transaction and prevout that the script will be ran against. This is fine for most scripts however this will make it so OP_CAT based covenants do not work because you are generating the signature in the script. The way to fix this would be to be able to provide the actual transaction and prevouts of the inputs into tapsim so they can be used to validate against instead of just having them randomly generated on the fly