feat: implement extSignTx function

[YukiTsuchida]

• Implemented Authenticator.sol and extSignTx().
• Implemented unit tests for extSignTx and its helper functions.

[github-actions]

Slither report

Summary

• calls-loop (1 results) (Low)

calls-loop

Impact: Low
Confidence: Medium

• ID-0
  TxAuthManager._verifySignatures(bytes32,Account.Data[],bytes[]) has external calls inside a loop: (ok,ret) = address(verifier).staticcall(callData)
  Calls stack containing the loop:
  Authenticator.extSignTx(MsgExtSignTx.Data)

cross-solidity/src/core/TxAuthManager.sol

Lines 84 to 126 in c1dfcf8

	function _verifySignatures(bytes32 txIDHash, Account.Data[] calldata signers, bytes[] calldata signatures)
	internal
	view
	virtual
	override
	{
	uint256 len = signers.length;
	if (len != signatures.length) {
	revert SignerCountMismatch(len, signatures.length);
	}
	if (len > MAX_SIGNERS_PER_TX) {
	revert TooManySigners(len, MAX_SIGNERS_PER_TX);
	}
	CrossStore.AuthStorage storage s = _getAuthStorage();
	for (uint256 i = 0; i < len; ++i) {
	Account.Data calldata signer = signers[i];
	if (signer.auth_type.mode != AuthType.AuthMode.AUTH_MODE_EXTENSION) {
	revert AuthModeMismatch();
	}
	string calldata typeUrl = signer.auth_type.option.type_url;
	IAuthExtensionVerifier verifier = s.authVerifiers[typeUrl];
	if (address(verifier) == address(0)) {
	revert VerifierNotFound(typeUrl);
	}
	bytes memory callData =
	abi.encodeWithSelector(IAuthExtensionVerifier.verify.selector, txIDHash, signer, signatures[i]);
	(bool ok, bytes memory ret) = address(verifier).staticcall(callData);
	if (!ok) {
	revert VerifierStaticCallFailed(typeUrl);
	}
	bool verified = abi.decode(ret, (bool));
	if (!verified) {
	revert VerifierReturnedFalse(txIDHash, typeUrl);
	}
	}
	}

[github-actions]

LCOV of commit f570a30 during Coverage Report #98

Summary coverage rate:
  lines......: 98.5% (270 of 274 lines)
  functions..: 100.0% (50 of 50 functions)
  branches...: no data found

Files changed coverage rate:
                                         |Lines       |Functions  |Branches    
  Filename                               |Rate     Num|Rate    Num|Rate     Num
  =============================================================================
  src/core/Authenticator.sol             |16.7%     24| 0.0%     4|    -      0
  src/core/CrossModule.sol               |39.3%     28| 0.0%    11|    -      0
  src/core/CrossSimpleModule.sol         |28.6%      7| 0.0%     2|    -      0
  src/core/CrossStore.sol                | 100%      3| 0.0%     3|    -      0
  src/core/TxAuthManager.sol             |11.5%     78| 0.0%     9|    -      0
  src/example/SampleEcrecoverVerifier.sol|14.3%      7| 0.0%     1|    -      0

Full coverage report