This is a refactoring PR to simplify our environment loading code by:

- Getting rid of `EnvironmentErrorMessage` in favor of using
`anyhow::Result` everywhere, with a separate `mpsc` channel to
communicate statuses that will be shown in the activity indicator
- Inlining some functions that were only called once to reduce
indirection
- Removing the separate `direnv` module

Release Notes:

- N/A