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/integration/test_preflight.py

@@ -94,14 +94,14 @@ def _seed_protocol_source(source):
 class TestProtocol:
     @pytest.mark.ci
     def test_protocol_current_version_accepted(self, shared_server):
-        """--protocol=2.23.0 (the current PROTOCOL_VERSION) is accepted and the
+        """--protocol=2.25.0 (the current PROTOCOL_VERSION) is accepted and the
         transfer completes normally."""
         source = os.path.join(TEST_DATA_DIR, "proto_ok_src")
         dest = os.path.join(TEST_DATA_DIR, "proto_ok_dst")
         shutil.rmtree(dest, ignore_errors=True)
         os.makedirs(dest)
         _seed_protocol_source(source)
-        result, _ = run_client(source, dest, flags=["--protocol=2.23.0"],
+        result, _ = run_client(source, dest, flags=["--protocol=2.25.0"],
                                port=shared_server.port)
         assert result.returncode == 0, \
             f"--protocol current run failed: {(result.stderr or result.stdout)[:400]}"