Support parallel restore (jobs) for basebackup in barman-cloud plugin

Currently, the barman-cloud plugin supports parallelism for:

backup (data.jobs)
WAL restore (wal.maxParallel)

However, basebackup restore via barman-cloud-restore appears to run single-threaded.

For large databases, this creates a significant performance bottleneck during recovery.

Start at the barman-cloud-restore entry point and compare how existing data.jobs backup parallelism and wal.maxParallel WAL restore are handled. Determine how basebackup restore currently executes, then verify that it accepts and uses parallel jobs so large database recovery is no longer single-threaded.

Written by the indexing model from the issue text.