ci: Add Hardhat tooling integration test (#516)

## Description

Adds a CI workflow that builds a small Hardhat project with
`hardhat-polkadot`, exercising the standard JSON interface between
`resolc` and `hardhat-polkadot` end-to-end.

## Resolved Issues

Closes #514

tooling-projects/hardhat/erc20/hardhat.config.js

@@ -0,0 +1,33 @@
+require("@nomicfoundation/hardhat-toolbox");
+require("@parity/hardhat-polkadot");
+
+const RESOLC_PATH_ENV_NAME = "RESOLC_PATH";
+
+function getEnv(name) {
+    const value = process.env[name];
+    if (!value) {
+        throw new Error(`Required environment variable '${name}' is missing`);
+    }
+
+    return value;
+}
+
+/** @type {import('hardhat/config').HardhatUserConfig} */
+module.exports = {
+    solidity: "0.8.35",
+    resolc: {
+        compilerSource: "binary",
+        settings: {
+            resolcPath: getEnv(RESOLC_PATH_ENV_NAME),
+            optimizer: {
+                enabled: true,
+                parameters: "z"
+            },
+        },
+    },
+    networks: {
+        hardhat: {
+            polkadot: true
+        },
+    },
+};