feat(stats): populate receiver wire counters on both receive paths

The single-threaded and -m receivers never populated ReceiverStats.matched_data
or .deleted_files, so --stats always printed 0 for both even when rsync
reported nonzero.  Track the bytes reconstructed from the basis file while
applying a delta, and tally the delete-commit counts (manifest and
per-directory sessions) into the receiver stats.  The -m pipeline now carries
its own stats/would-delete fields and emits the STATUS_STATS frame before the
terminal success, so --threads finally reports the counters and renders
-n --delete  lines.

Also normalize the -n --delete would-delete enumeration's absolute basis
prefixes exactly like the real commit path (fixing an over-report) and fix the
basis_delete_relative off-by-one when the receive root is '/'.  Unit tests
cover the root mapping and the basis protection; integration tests cover
matched/deleted stats for both receivers and the --threads dry-run delete
lines.

src/shared/delete_plan.c

@@ -444,6 +444,10 @@ bool delete_plan_session_limit_reached(const DeletePlanSession* session) {
   return session && session->limit_hit;
 }
 
+size_t delete_plan_session_deleted(const DeletePlanSession* session) {
+  return session ? session->deleted : 0;
+}
+
 /* True for a destination-relative path section entry (non-empty, relative,
  * traversal-free). */
 static bool valid_rel_path(const char* value) {