feat: add ERC721Soulbound contract

Author: aj-may

contracts/ERC721Soulbound.sol

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.4;
+
+import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
+
+abstract contract ERC721Soulbound is ERC721 {
+    function _beforeTokenTransfer(
+        address from,
+        address to,
+        uint256 tokenId,
+        uint256 batchSize
+    ) internal virtual override {
+        require(from == address(0) || to == address(0), "ERC721Soulbound: token is non-transferable");
+        super._beforeTokenTransfer(from, to, tokenId, batchSize);
+    }
+}