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/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "erc20-hardhat",
+  "private": true,
+  "devDependencies": {
+    "@nomicfoundation/hardhat-toolbox": "^5.0.0",
+    "@parity/hardhat-polkadot": "^0.3.0",
+    "hardhat": "^2.26.0"
+  },
+  "dependencies": {
+    "@openzeppelin/contracts": "^5.3.0"
+  }
+}