Add tests for the ERC20 implementation with EIP-2612 permit coverage

test/ERC20/ERC20Mock.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.30;
+
+import {ERC20Facet} from "../../src/ERC20/ERC20/ERC20Facet.sol";
+import {LibERC20} from "../../src/ERC20/ERC20/libraries/LibERC20.sol";
+
+/// @title ERC20Mock
+/// @notice Helper contract that extends ERC20Facet and exposes mint function for testing.
+/// @dev This contract is NOT part of the library. It exists solely to enable testing of ERC20Facet functionality.
+contract ERC20Mock is ERC20Facet {
+    /// @notice Mints tokens to address.
+    /// @dev External function for LibERC20.mint() to enable testing.
+    /// @param _to Address to receive minted tokens.
+    /// @param _amount Amount of tokens to mint.
+    function mint(address _to, uint256 _amount) external {
+        LibERC20.mint(_to, _amount);
+    }
+
+    /// @notice Initializes the ERC20 token with name, symbol, and decimals.
+    /// @dev Sets up storage for testing.
+    /// @param _name Token name.
+    /// @param _symbol Token symbol.
+    /// @param _decimals Token decimals.
+    function initialize(string memory _name, string memory _symbol, uint8 _decimals) external {
+        LibERC20.ERC20Storage storage s = LibERC20.getStorage();
+        s.name = _name;
+        s.symbol = _symbol;
+        s.decimals = _decimals;
+    }
+}