feat(parity): wire-stats protocol 2.25.0 + out-format %b/%c/%C

Bump PROTOCOL_VERSION to 2.25.0 and append a report_stats bool to the
config frame, add a STATUS_STATS status, and add process-wide wire byte
counters (protocol_bytes_written/read) for the client.

Render the rsync 3.4.1 --out-format %b (wire bytes sent) and %c (wire
bytes read back) tokens from per-file counter deltas, and %C (whole-file
xxh128 checksum, seed 0) via a new streaming checksum_digest_file().

tests/test_fuzz_smoke.c

@@ -18,9 +18,10 @@
 
 /* P8 config-frame tail: super_mode (4) + copy-as presence (4) + uid (4) + gid (4). */
 #define P8_TAIL_BYTES 16
-/* Protocol 2.23.0 appends one trailing bool (report_dest_info) AFTER the P8
- * tail, so the P8 fields sit this many bytes before the end of the frame. */
-#define OUTPUT_TAIL_BYTES 4
+/* Protocol 2.25.0 appends two trailing bools (report_dest_info, report_stats)
+ * AFTER the P8 tail, so the P8 fields sit this many bytes before the end of the
+ * frame. */
+#define OUTPUT_TAIL_BYTES 8
 
 /* Smoke test for chunk_deserialize fuzz target */
 static void test_fuzz_chunk_deserialize() {