fix(parity): init delete_suppressed; gate deleted-path retention

- Initialize PipelineContextSender.delete_suppressed=false: an uninitialized
  true silently skipped the --delete keep-set manifest under -m/--threads,
  so destination extras were never removed.
- Allocate/install the receiver deleted-path observer only when
  report_deletes is set (--info=del / -i / --out-format under --delete), cap
  the retained list at MAX_MANIFEST_ENTRIES, and free already-created lists
  on the receiver-pipeline create failure path.
- Validate report_deletes/report_stats/report_dest_info on receive.
- Correct stale comments (config.h report_deletes, delete_plan.h deleted
  count, multiprocessing.h stats locking, utils.h observer placement).
- Tests: sender delete_suppressed init, report_deletes gating (unit), and
  -m/--delete default delete-after keep-set removal (integration).

src/shared/utils.h

@@ -134,6 +134,11 @@ bool path_under_skip_prefix(const char* child_rel, bool at_root, const DeleteSki
    cap and returns DELETE_WALK_LIMIT_REACHED when more extras remained.
    `deleted_out`/`skipped_out` optionally receive the number of entries removed
    and the number skipped because of the cap. */
+DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
+                                       const ArrayList* synced_dirs, size_t max_delete,
+                                       const DeleteSkipEntry* skips, int skip_count,
+                                       size_t* deleted_out, size_t* skipped_out);
+
 /* Optional per-deletion observer: called for each destination-relative path
    actually removed (a file, symlink, or directory), in removal order, so the
    receiver can stream rsync's `--info=del`/`--info=remove` lines. */
@@ -147,11 +152,6 @@ DeleteWalkResult delete_extras_limited_observed(const char* dest_root, const Arr
                                                 size_t* deleted_out, size_t* skipped_out,
                                                 DeletePathObserver observer,
                                                 void* observer_context);
-
-DeleteWalkResult delete_extras_limited(const char* dest_root, const ArrayList* manifest,
-                                       const ArrayList* synced_dirs, size_t max_delete,
-                                       const DeleteSkipEntry* skips, int skip_count,
-                                       size_t* deleted_out, size_t* skipped_out);
 /* Read-only companion to delete_extras_limited: walk the destination exactly as
    the delete pass would and APPEND (strdup'd) destination-relative paths that
    WOULD be removed, without touching disk.  Used for -n/--dry-run --delete