Stop serializing HH config data we don't need

[gnidan]

PR description

As raised by @emilyJLin95, this PR fixes a problem where hre.config now contains non-serializable data. Since @truffle/from-hardhat needs only a small portion of the data in hre.config, this PR takes the approach to pre-process it, whittling it down to just what we need. This prevents serialization issues that may arise.

Testing instructions

In repo root:

git checkout fix/from-hardhat-bigints
yarn
cd packages/from-hardhat && yarn link && cd -

In a new directory for a fresh HH project:

npx hardhat # follow the wizard, the wonderful wizard
npx hardhat compile
yarn link @truffle/from-hardhat
node

In that node repl that just started:

const FromHardhat = require("@truffle/from-hardhat");
await FromHardhat.prepareConfig();

Observe that it does not break.

Oh, and you'll need the latest Node.js if you want that await to work.

Documentation

• I thought about documentation and added the doc-change-required label to this PR if documentation updates are required.

Breaking changes and new features

• I have added any needed breaking-change and new-feature labels for the appropriate packages.

[gnidan]

cc @alcuadrado in case it was an accident that hre.config is no longer serializable

[cds-amal]

Looks good to me!