Function getP2SHInputSize

Calculates the input size for a P2SH input including script size. Base input: prevhash (32) + prevIndex (4) + script length (varint) + script size + sequence (4)

According to Bitcoin Optech calculator (https://bitcoinops.org/en/tools/calc-size/):

• P2SH 2-of-3 scriptSig: 254 bytes
• Format: OP_0 OP_PUSH72 <ecdsa_signature> OP_PUSH72 <ecdsa_signature> OP_PUSHDATA1 105 <OP_2 OP_PUSH33 OP_PUSH33 OP_PUSH33 OP_3 OP_CHECKMULTISIG>