It seems easier for contributors to get started if the compiler version is already configured; plus, this will presumably make it so that I don't have to set the Rust version with `rustup override` whenever I create a new worktree.

This should have been done from the beginning, since we operate on these symbols in several places for formatting. This would also help a migration away from `cursive`, since now only two modules have direct dependencies on `cursive`/`cursive_core`:

- git-branchless-lib for general output formatting.
- git-branchless-undo for the interactive undo UI.

Currently, `git submit` for Phabricator will abort the entire operation if any commit fails to be submitted. This means that if `arc diff` succeeds on one commit and then fails on its child, the entire operation is aborted. However, the first `arc diff` had side effects, so the user gets diffs uploaded to Phabricator that are not reflected locally. Instead, we should confirm any passing commits and abort after we get a failing commit. This commit updates the Phabricator forge to handle the error case better and not produce garbage commits on Phabricator.

…e management

…remote, instead of all remotes