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/server/receiver_pipeline.h

@@ -54,6 +54,13 @@ typedef struct PipelineContextReceiver {
      directory entries.  Only write_thread mutates it (before it joins); the
      caller (server.c) applies it after the delete/delay-updates phase. */
   DirTimeList dir_times;
+  /* End-of-transfer wire counters (protocol 2.25.0).  receive_thread accumulates
+     matched_data under `mutex`; server.c adds the delete-commit tallies after
+     both threads join and emits the STATUS_STATS frame. */
+  ReceiverStats stats;
+  /* -n/--dry-run --delete would-delete path list, collected by receive_thread
+     and reported in the STATUS_STATS frame. */
+  struct ArrayList* would_delete;
 } PipelineContextReceiver;
 
 PipelineContextReceiver* pipeline_context_receiver_create(Config* config, Queue* queue_receiver,