No support for custom tuples

[ashish10677]

Problem

If we want to generate a merkle tree with a custom datatype:

const tree = StandardMerkleTree.of(values, ["bytes4", "tuple(uint256 chainId, uint256 amount, address target, bytes values)"]);

The current implementation doesn't support it.
It fails because the function AbiPack doesn't accept components which is required while creating argument type.

typ, err := abi.NewType(v, "string", nil)

openzeppelin-merkle-tree-go/standard_merkle_tree/solidity_utils.go

Line 18 in cba4971

typ, err := abi.NewType(v, "string", nil)

Instead of passing nil, for tuple type we need to pass the components of type []abi.ArgumentMarshaling