Expanders followup

[voltrevo]

Dependent PR

This PR depends on:

• Add expander for registration #555

That PR should be merged first.

What is this PR doing?

Addresses comments on previous PRs:

• Avoids underscores in typechain factories (comment)
• Adds docs to some key exported classes (comment)

How can these changes be manually tested?

yarn hardhat test (No functionality changes expected)

Does this PR resolve or contribute to any issues?

Nope

Checklist

• I have manually tested these changes
• Post a link to the PR in the group chat

Guidelines

• If your PR is not ready, mark it as a draft
• The resolve conversation button is for reviewers, not authors
  • (But add a 'done' comment or similar)