feat(delete): per-directory delete plans for --delete-during/--delete-delay (protocol 2.24.0)

Stream one delete plan per source directory from sender to receiver instead of
a single whole-tree keep-set manifest:

- --delete-during applies each directory's extras as its plan arrives, before
  that directory's data (rsync's generator-order deletion).
- --delete-delay snapshots each directory's extras while the plan arrives and
  commits the removals only after a fully-successful transfer, so files created
  after the scan survive (matching rsync's delete-delay, not delete-after).
- Type conflicts (a destination file blocking a source directory, or vice
  versa) are cleared immediately in both modes, so the nested write succeeds.

The plan carries the destination-relative directory, its kept child directory
names and its kept child file names; the first frame also carries the global
protected prefixes, size-skipped prefixes and --delete-missing-args paths.
--delete-before keeps the existing whole-tree early manifest; plain --delete and
--delete-after keep the end-of-transfer manifest commit.

Preserves the existing safety surface: protected/size-skipped prefixes and the
--delay-updates/basis skips are honored at any depth, deletion is scoped to the
synchronized directories (--files-from), MAX_SERVER_DELETE_COUNT and
--max-delete (partial + exit 25) are shared across plans, symlinks are never
followed, and paths are confined to the receive root.

src/server/server.c

@@ -962,6 +962,20 @@ void handler(int file_descriptor) {
         delete_manifest_free(context->deferred_manifest);
         context->deferred_manifest = NULL;
       }
+      /* --delete-delay: receive_thread snapshotted each plan's extras as it
+         arrived; with the disk writer drained, commit the deferred removals.
+         --delete-during already applied its plans on the receive thread. */
+      if (context->deferred_plans) {
+        DeleteCommitResult deletion =
+            delete_plan_session_commit(context->deferred_plans, config);
+        if (deletion == DELETE_COMMIT_ERROR) {
+          transfer_ok = false;
+        } else if (deletion == DELETE_COMMIT_LIMIT_REACHED) {
+          context->delete_limit_reached = true;
+        }
+        delete_plan_session_destroy(context->deferred_plans);
+        context->deferred_plans = NULL;
+      }
     }
     if (transfer_ok && !config->dry_run) {
       /* --delay-updates: receive_thread has finished the whole protocol stream