Support P2TR in output parsing

[gregdhill]

As in the title we need to support P2TR here:

bitcoin-spv/src/BTCUtils.sol

Lines 578 to 626 in 8f37525

	function extractHashAt(
	bytes memory _output,
	uint256 _at,
	uint256 _len
	) internal pure returns (bytes memory) {
	uint8 _scriptLen = uint8(_output[_at]);
	// don't have to worry about overflow here.
	// if _scriptLen + 1 overflows, then output length would have to be < 1
	// for this check to pass. if it's < 1, then we errored when assigning
	// _scriptLen
	if (_scriptLen + 1 != _len) {
	return hex"";
	}
	if (uint8(_output[_at + 1]) == 0) {
	if (_scriptLen < 2) {
	return hex"";
	}
	uint256 _payloadLen = uint8(_output[_at + 2]);
	// Check for maliciously formatted witness outputs.
	// No need to worry about underflow as long b/c of the `< 2` check
	if (_payloadLen != _scriptLen - 2 || (_payloadLen != 0x20 && _payloadLen != 0x14)) {
	return hex"";
	}
	return _output.slice(_at + 3, _payloadLen);
	} else {
	bytes3 _tag = _output.slice3(_at);
	// p2pkh
	if (_tag == hex"1976a9") {
	// Check for maliciously formatted p2pkh
	// No need to worry about underflow, b/c of _scriptLen check
	if (uint8(_output[_at + 3]) != 0x14 ||
	_output.slice2(_at + _len - 2) != hex"88ac") {
	return hex"";
	}
	return _output.slice(_at + 4, 20);
	//p2sh
	} else if (_tag == hex"17a914") {
	// Check for maliciously formatted p2sh
	// No need to worry about underflow, b/c of _scriptLen check
	if (uint8(_output[_at + _len - 1]) != 0x87) {
	return hex"";
	}
	return _output.slice(_at + 3, 20);
	}
	}
	return hex""; /* NB: will trigger on OPRETURN and any non-standard that doesn't overrun */
	}