perf: sync fork streams what a device lacks, and writes in shared spaces

The sync fork moves to the signed tip of halkyon/space-writes, which
brings two branches:

- halkyon/streamed-collection: the server hands each change a device
  lacks out as it is read, so a device hears from it at once; a large
  first sync had outlasted the client's 40 s before the server sent
  anything, and started over each time.
- halkyon/space-writes (ADR 0044, D24): a write without a transaction
  acts in the space it touches, and the host names where a new row goes
  (`newRowSpace`), each through transactionForUser, which checks
  membership and role. Nothing names one yet.

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

@@ -1888,8 +1888,8 @@ packages:
     dependency: "direct overridden"
     description:
       path: "packages/serverpod_offline_sync"
-      ref: "741e334d6ac4ca89f99945dda2e444152ee32994"
-      resolved-ref: "741e334d6ac4ca89f99945dda2e444152ee32994"
+      ref: "845fb557db3e21cf78b152f9e39ba6a26947bab9"
+      resolved-ref: "845fb557db3e21cf78b152f9e39ba6a26947bab9"
       url: "https://code.halkyon.app/project-halkyon/serverpod-offline-sync.git"
     source: git
     version: "0.0.10"