Add a --progress progress-bar option

[rolandwalker]

Description

Add a --progress progress-bar option which only works in conjunction with --batch, not STDIN, as it needs to read over the file to count the number of goal statements.

Care is also taken that a plain file, not a FIFO, is passed to --batch.

Incidentally convert a neighboring string to triple quotes since it contained both single and double quotes.

Motivation: the bar might be pretty, but the real value-add for big jobs is the ETA on the right.

Followups: the new code should really go into a batch.py, but that is awaiting a refactor of the CLI arguments.

Example:

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

No correctness or security regressions stood out in the PR diff (c1ef3d8...c5b535e).

Residual test gaps I’d still address:

1. --progress fallback path is untested when stderr is not a TTY, even though behavior changes at main.py.
   Add a test to assert it still executes batch statements normally (without progress) and exits 0.

2. --progress with --batch - (stdin batch input) is untested; current logic skips the progress branch entirely at main.py.
   Add a test to lock expected behavior (silent fallback vs warning), so future changes don’t regress UX.

3. Error handling in the pre-count pass (ValueError from parser) is not covered for progress mode at main.py.
   Add a test with an overlong multiline statement to verify the intended error message and non-zero exit.

I couldn’t run pytest locally because pytest is not installed in this environment (command not found).