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/file_receive.h

@@ -142,6 +142,10 @@ typedef enum {
    do or everything committed, DELETE_COMMIT_LIMIT_REACHED when the budget
    stopped part of the work, or DELETE_COMMIT_ERROR on a genuine failure. */
 DeleteCommitResult manifest_delete_all(const Config* config, DeleteManifest* manifest);
+/* Like manifest_delete_all, but reports how many destination entries the commit
+   removed (for the end-of-transfer wire stats).  `deleted` may be NULL. */
+DeleteCommitResult manifest_delete_all_counted(const Config* config, DeleteManifest* manifest,
+                                               size_t* deleted);
 
 /* -n/--dry-run --delete would-delete reporting: walk the destination exactly as
    the delete pass would and append (strdup'd) destination-relative paths that
@@ -150,6 +154,10 @@ DeleteCommitResult manifest_delete_all(const Config* config, DeleteManifest* man
    clean walk; `*count_out` receives the number of paths appended. */
 bool manifest_would_delete_list(const Config* config, DeleteManifest* manifest, ArrayList* out,
                                 size_t* count_out);
+/* Convert one basis-directory path to the receive-root-relative protection
+   prefix the delete walker uses (NULL when it lies outside the root).  Exposed
+   for unit tests of the root-of-"/" and normalization edge cases. */
+char* file_receive_basis_delete_relative(const Config* config, const char* path);
 
 /* Outcome of a single file_save_to_disk operation.  The receiver needs to
    distinguish "written" from "skipped" so --remove-source-files can be told