Add subcommand to prune Cavalcade tables

Importing a database export which contains Cavalcade tables will kick off a process where your local machine tries to run all of the cron jobs from the time the export was taken up to the current date.

These jobs can likely be safely removed, and it would be good to add a subcommand to prune all old cron and cavalcade entries.

No files, tests, or command entry points are named. Start by inspecting the repository's existing WP-CLI commands and any references to cron and Cavalcade tables, then clarify which entries count as old and how pruning should be invoked. Done means the new subcommand safely removes the requested obsolete cron and Cavalcade entries and has coverage for that behavior.

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