A compact size unsigned integer representing the number of leaf hashes, followed by a list
of leaf hashes, followed by the 4 byte master key fingerprint concatenated with the
derivation path of the public key. The derivation path is represented as 32-bit little
endian unsigned integer indexes concatenated with each other. Public keys are those needed
to spend this output. The leaf hashes are of the leaves which involve this public key. The
internal key does not have leaf hashes, so can be indicated with a hashes len of 0.
Finalizers should remove this field after PSBT_IN_FINAL_SCRIPTWITNESS is constructed.