perf(sync): the fork's signed commit with inbound merges and fast deletes

The offline sync package's shared part now comes from the fork's branch
halkyon/fast-deletes (b545035, signed), which stacks two changes on the
byte payload fix: onInboundMerge, called only when changes from the
remote peer were merged, which the app now reads again on rather than
after every save's sync; and local deletes that skip the foreign key
projection pass when it can't change it (8 s for one delete in a library
of 8,000 cards, 30 s for a card, now tens of milliseconds).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

pubspec.lock

@@ -1578,8 +1578,8 @@ packages:
     dependency: "direct overridden"
     description:
       path: "packages/serverpod_offline_sync"
-      ref: "1dce863e72e57eb51222452dd9baf1bbd7c4384e"
-      resolved-ref: "1dce863e72e57eb51222452dd9baf1bbd7c4384e"
+      ref: b5450353b98240a1bd6f4471815a8be94c91ce5b
+      resolved-ref: b5450353b98240a1bd6f4471815a8be94c91ce5b
       url: "https://code.halkyon.app/project-halkyon/serverpod-offline-sync.git"
     source: git
     version: "0.0.10"