function extractPartialSigs(input) {
  let pSigs = [];
  if ((input.partialSig || []).length === 0) {
    if (!input.finalScriptSig && !input.finalScriptWitness) return [];
    pSigs = getPsigsFromInputFinalScripts(input);
  } else {
    pSigs = input.partialSig;
  }
  return pSigs.map(p => p.signature);
}
Extracts the signatures from a PsbtInput object.
If the input has partial signatures, it returns an array of the signatures.
If the input does not have partial signatures, it checks if it has a finalScriptSig or finalScriptWitness.
If it does, it extracts the signatures from the final scripts and returns them.
If none of the above conditions are met, it returns an empty array.

@param input - The PsbtInput object from which to extract the signatures.
@returns An array of signatures extracted from the PsbtInput object.