refactor: remove OZ dependency in dispatch

certora/dispatch/ERC20Standard.sol

@@ -1,8 +1,42 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 pragma solidity ^0.8.0;
 
-import {ERC20} from "../../lib/openzeppelin-contracts/contracts/token/ERC20/ERC20.sol";
+contract ERC20Standard {
+    address public owner;
+    uint256 public totalSupply;
+    mapping(address => uint256) public balanceOf;
+    mapping(address => mapping(address => uint256)) public allowance;
 
-contract ERC20Standard is ERC20 {
-    constructor(string memory name, string memory symbol) ERC20(name, symbol) {}
+    constructor() {
+        owner = msg.sender;
+    }
+
+    modifier onlyOwner() {
+        require(msg.sender == owner);
+        _;
+    }
+
+    function _transfer(address _from, address _to, uint256 _amount) internal returns (bool) {
+        balanceOf[_from] -= _amount;
+        balanceOf[_to] += _amount;
+        return true;
+    }
+
+    function transfer(address _to, uint256 _amount) public returns (bool) {
+        return _transfer(msg.sender, _to, _amount);
+    }
+
+    function transferFrom(address _from, address _to, uint256 _amount) public returns (bool) {
+        allowance[_from][msg.sender] -= _amount;
+        return _transfer(_from, _to, _amount);
+    }
+
+    function approve(address _spender, uint256 _amount) public {
+        allowance[msg.sender][_spender] = _amount;
+    }
+
+    function mint(address _receiver, uint256 _amount) public onlyOwner {
+        balanceOf[_receiver] += _amount;
+        totalSupply += _amount;
+    }
 }

certora/dispatch/ERC20USDT.sol

@@ -2,10 +2,8 @@
 pragma solidity ^0.8.0;
 
 contract ERC20USDT {
-    uint256 public constant MAX_UINT = 2 ** 256 - 1;
-
-    uint256 public totalSupply;
     address public owner;
+    uint256 public totalSupply;
     mapping(address => uint256) public balanceOf;
     mapping(address => mapping(address => uint256)) public allowance;
 
@@ -28,7 +26,7 @@ contract ERC20USDT {
     }
 
     function transferFrom(address _from, address _to, uint256 _amount) public {
-        if (allowance[_from][msg.sender] < MAX_UINT) {
+        if (allowance[_from][msg.sender] < type(uint256).max) {
             allowance[_from][msg.sender] -= _amount;
         }
         _transfer(_from, _to, _amount);