Extract CLI to separate opencage-cli package

[sbscully]

Summary

• The opencage CLI tool has been extracted to its own repository and PyPI package: opencage-cli. This PR removes the duplicated code from this repo.
• Deletes opencage/command_line.py, opencage/batch.py, their tests/fixtures, and examples/batch.py + examples/addresses.csv + batch-progress.gif.
• Drops tqdm and certifi from dependencies (only used by the batch CLI) and removes the [project.scripts] entry point.
• Bumps version to 3.4.0 and adds a Changes.txt entry pointing users to pip install opencage-cli.
• README's CLI section is replaced with a one-line pointer to the new repo.

The library API is unchanged; opencage-cli already depends on this package and only imports OpenCageGeocode / OpenCageGeocodeError from opencage.geocoder, both of which remain exported.

User-visible breaking change: anyone relying on pip install opencage to provide the opencage CLI command will need to switch to pip install opencage-cli after this release.