Integration test fixes: reconcile SyncTypeFlags phantom-bit assertions and sync-round counts

- SyncTypeFlags phantom-bit tests used bits 8/9/10 as unmapped examples;
  board/prekey/group now map those, so use bits 11+ (still unmapped).
- rawValueInitNormalizesPhantomBits: highest known bit is now 10, so the
  flags serialize to 2 bytes, not 1.
- Board/fragment/announce sync tests silence the prekey round (added by the
  prekeys feature; default 60s schedule fires at the maintenance barrier).
- DiagnosticsMockContext: conform to the CommandContextProvider members added
  by private-groups (group*) and cashu-chips (sendPublicMessage).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bitchatTests/Sync/GossipSyncBoardTests.swift

@@ -34,6 +34,9 @@ struct GossipSyncBoardTests {
         config.messageSyncIntervalSeconds = 0
         config.fragmentSyncIntervalSeconds = 0
         config.fileTransferSyncIntervalSeconds = 0
+        // Silence the prekey round (added by the prekeys feature; groupMessage
+        // rides the message schedule, already off) so board is isolated.
+        config.prekeyBundleSyncIntervalSeconds = 0
         return config
     }