feat: Add foundry environment and CI

foundry/src/Counter.sol

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.13;
+
+contract Counter {
+    uint256 public number;
+
+    function setNumber(uint256 newNumber) public {
+        number = newNumber;
+    }
+
+    function increment() public {
+        number++;
+    }
+}