enable hardhat coverage

[mshakeg]

It would be good to enable hardhat coverage in this template repo as a PoC.

I just went through the exercise on a project utilising this template and had to do the following to get hardhat coverage to work:

1. install and import @nomicfoundation/hardhat-toolbox in hardhat.config.ts
2. Install all the external libs/pkgs in ./lib using your project's node package manager(i.e. yarn, npm or pnpm) and ensure that these packages are now visible in the package.json and node_modules
3. before running hardhat coverage you'll first have to comment out the preprocess config in the HardhatUserConfig to disable it