ref(cli): make attach-partitions output legible for long runs

[onewland]

attach-partitions walks partitions one at a time and can run for a long
time, but its progress output was hard to act on. Two commits fix that.

State the mode and tables

The output never said whether a run was a dry run, so the only signal was
the wording of each line, and Would attach partition 90-20240212 named
neither the source nor the destination. Reading a scrollback, you could not
tell a rehearsal from a real attach, or which tables were involved.

The mode and table pair are now announced before any work, and every
partition line is qualified with both tables.

Add timestamps

Progress went through click.echo, so no line carried a timestamp. On a long
run there was no way to tell how long an individual ATTACH took, or when a
run stalled.

The output now goes through a module logger, matching the convention in the
rest of snuba.cli. LOG_FORMAT is "%(asctime)s %(message)s", so lines are
timestamped:

2026-09-03 12:48:40,815 [EXECUTE] Attaching partitions from d.src to d.dst
2026-09-03 12:48:40,815 Attached partition 90-20260608 from d.src to d.dst
2026-09-03 12:48:40,815 [EXECUTE] Attached 1 partition(s) from d.src to d.dst

Behaviour changes to be aware of

Moving to logging has two consequences beyond formatting:

• Output moves from stdout to stderr, since logging.basicConfig installs
  a StreamHandler on stderr. This would break any pipeline parsing this
  command's stdout. I am not aware of one, but say the word and I will attach a
  stdout handler instead.
• --log-level now gates these lines, so --log-level WARNING silences
  progress output.

Also worth a look: a --partition-id run now logs twice per partition, because
attach_partition_from_table already emits its own "Attaching partition" line.
Previously the two went to different streams so the overlap was invisible. Happy
to drop the CLI line or demote the library one to debug.

Testing

tests/clickhouse/test_partition_management.py passes (43 tests); mypy and the
pre-commit ruff hooks are clean. No test asserted on this CLI's output before
or after.