Refactor per-channel output and add tests for fetch_all_channels

[DarshanCode2005]

# FIXME(@fricklerhandwerk): Fold that intobranch_info, so there's only one output. print("Parallel fetches results", results)
What’s changed:

• Cleaner output: Each channel now prints one clear line with its details (release, state, commit) and result (fetched, already present, or error), after all fetches finish.
• Standard output: Replaced print/pprint with self.stdout.write for proper command output handling.
• Tests added:
  • 4 unit tests for reporting logic
  • 1 integration test for the full command flow with the database