feat(token): add minimal erc20 token implementation

src/Erc20.sol

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.36;
+
+/// @title Minimal, correct ERC20 base shared by the LP token and test tokens.
+contract Erc20 {
+    event Transfer(address indexed from, address indexed to, uint256 value);
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+
+    string public name;
+    string public symbol;
+    uint8 public constant decimals = 18;
+
+    uint256 public totalSupply;
+    mapping(address => uint256) public balanceOf;
+    mapping(address => mapping(address => uint256)) public allowance;
+
+    constructor(string memory tokenName, string memory tokenSymbol) {
+        name = tokenName;
+        symbol = tokenSymbol;
+    }
+
+    function _mint(address to, uint256 value) internal {
+        totalSupply += value;
+        balanceOf[to] += value;
+        emit Transfer(address(0), to, value);
+    }
+
+    function _burn(address from, uint256 value) internal {
+        balanceOf[from] -= value;
+        totalSupply -= value;
+        emit Transfer(from, address(0), value);
+    }
+
+    function _transfer(address from, address to, uint256 value) internal {
+        balanceOf[from] -= value;
+        balanceOf[to] += value;
+        emit Transfer(from, to, value);
+    }
+
+    function approve(address spender, uint256 value) external returns (bool) {
+        allowance[msg.sender][spender] = value;
+        emit Approval(msg.sender, spender, value);
+        return true;
+    }
+
+    function transfer(address to, uint256 value) external returns (bool) {
+        _transfer(msg.sender, to, value);
+        return true;
+    }
+
+    function transferFrom(address from, address to, uint256 value) external returns (bool) {
+        uint256 allowed = allowance[from][msg.sender];
+        if (allowed != type(uint256).max) {
+            allowance[from][msg.sender] = allowed - value;
+        }
+        _transfer(from, to, value);
+        return true;
+    }
+}

src/interfaces/IErc20.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity 0.8.36;
+
+interface IErc20 {
+    event Transfer(address indexed from, address indexed to, uint256 value);
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+
+    function name() external view returns (string memory);
+    function symbol() external view returns (string memory);
+    function decimals() external view returns (uint8);
+    function totalSupply() external view returns (uint256);
+    function balanceOf(address owner) external view returns (uint256);
+    function allowance(address owner, address spender) external view returns (uint256);
+    function approve(address spender, uint256 value) external returns (bool);
+    function transfer(address to, uint256 value) external returns (bool);
+    function transferFrom(address from, address to, uint256 value) external returns (bool);
+}