Formerly, we used metatables to get custom `Option` and `Result` objects
which were difficult to type properly, leading to a lot of `unknown` and
`any` casts.
This refactor fixes it by making extensions opt-in, where we import the
extension methods separately from the original implementations, thereby
allowing us to not have to typecast things everywhere.
* Updates the `update_tools` dev script to include logic for using the
GitHub API to fetch and write READMEs for bins.
* Also optionally accepts a GitHub token for authenticated requests
using the `$GITHUB_TOKEN` environment variable.
* Also moves dev script dependencies at root manifest into
`dev_dependencies`.