Prober: pipelined bodies, merge-first order, a probe cache across resets

- XoverClient.bodies: PROBE_PIPELINE (8) BODY commands per connection at
  once, replies read in order (one at a time it ran 3-10 articles/s on 6
  connections against a queue of 1M).
- Claims in tiers: lone files first, then par2 sets and archives of
  releases without a readable name (what the par2 merge needs), then those
  of readable releases.
- probe_cache: final answers by message-id (status, inspection with the
  16 KiB hash and par2 file list), PROBE_VERSION 2. A reset empties the
  probe queue, not the cache; recreated candidates of probed articles are
  answered from it without the news server.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/probe/inspect.ts

@@ -28,6 +28,9 @@ export interface Inspection {
 
 const HASH_BYTES = 16 * 1024
 
+/** The inspection's version: raised when inspect() changes, so probe_cache rows of an older one are read again. */
+export const PROBE_VERSION = 2
+
 /** Names kept per inspection: the catalog wants the content's name, not every volume's. */
 export const MAX_NAMES = 8
 const MAX_NAME_LENGTH = 200