chore: add .mocharc.json

This commit adds a `.mocharc.json` configuration file so that mocha
hardhat tests can be directly debugged in
[VScode](https://hardhat.org/hardhat-runner/docs/advanced/vscode-tests).

.mocharc.json

@@ -0,0 +1,7 @@
+{
+    "require": "hardhat/register",
+    "timeout": 40000,
+    "_": [
+        "test/**/*.ts"
+    ]
+}