Script execution via rust-bitcoin-scriptexec

https://github.com/BitVM/rust-bitcoin-scriptexec

The API for simple scripts could look something like: ```script::exec(`1 1 OP_ADD`) == [2]```

Or with a witness stack: ```script::exec(`2 OP_ADD`, [3]) == [5]```

Or with tx input context for signature operations: ```script::exec(`$alice_pk OP_CHECKSIG`, [$alice_sig], $tx:5)```