feat(parity): rsync 3.4.1 checksum/timeout/temp-dir/connectivity parity (#289 #295 #296)

#289 checksum/compression:
- -c/--checksum now implies the incremental content quick-check (without
  implying -t), so an unchanged file is skipped like rsync.
- --checksum-choice/--cc accepts xxh64/xxhash, xxh3, xxh128, md5 and auto;
  md4/sha1/none and the two-name form are rejected by name.
- --compress-choice/--zc rejects lz4/zlib/zlibx by name (zstd/none/auto kept).
- --checksum-seed=0 is randomized per transfer and sent on the wire.
- --skip-compress uses rsync 3.4.1's default suffix list; slash separators and
  dot-less suffixes are accepted.
- add --no-whole-file.

#295 timeouts/alloc/temp-dir:
- --timeout default 0 (disabled), --contimeout default 60; 0 disables both,
  plus --no-timeout/--no-contimeout.
- --max-alloc=0 means no allocation limit (was rejected).
- --temp-dir accepts any dir, requires it to exist, and falls back to a
  non-atomic copy on EXDEV instead of aborting.

#296 connectivity/daemon:
- -M/--remote-option is rejected for daemon/TCP destinations (SSH-only).
- --trust-sender clarified as receiver-local; server-path tests added.
- --stop-at accepts rsync's full date form (y-m-dTh:m etc.).

Adds unit and integration coverage; no wire-field change, PROTOCOL_VERSION stays
2.22.0.

tests/integration/test_stop.py

@@ -150,13 +150,36 @@ class TestStopAt:
         assert _received_files(received) == [], \
             f"expected nothing transferred, got {_received_files(received)}"
 
+    @pytest.mark.ci
+    def test_stop_at_rsync_date_form(self, shared_server):
+        """rsync's full date form (Y-M-DTh:m) is accepted; a deadline well in the
+        future lets the transfer complete normally."""
+        source, dest = _make("dateform")
+        _seed_source(source)
+        stamp = time.strftime("%Y-%m-%dT%H:%M", time.localtime(time.time() + 3600))
+        result, _ = run_client(source, dest, flags=[f"--stop-at={stamp}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, \
+            f"--stop-at={stamp} should be accepted: " \
+            f"{(result.stderr or result.stdout)[:400]}"
+        received = get_dest_received_dir(dest, source)
+        mismatches, missing = verify_transfer(source, received)
+        assert not mismatches and not missing
+
+        # The slash-separated date spelling is accepted too.
+        slash = time.strftime("%Y/%m/%dT%H:%M", time.localtime(time.time() + 3600))
+        result, _ = run_client(source, dest, flags=[f"--stop-at={slash}"],
+                               port=shared_server.port)
+        assert result.returncode == 0, f"--stop-at={slash} should be accepted"
+
     @pytest.mark.ci
     def test_stop_rejects_garbage(self, shared_server):
         """Malformed --stop-at/--stop-after values are rejected up front."""
         source, dest = _make("garbage")
         _seed_source(source)
-        for flag in ("--stop-after=abc", "--stop-at=12:99", "--stop-at=12",
-                     "--stop-at=now+5x", "--stop-at=now-5s"):
+        for flag in ("--stop-after=abc", "--stop-at=12:99", "--stop-at=1234",
+                     "--stop-at=now+5x", "--stop-at=now-5s",
+                     "--stop-at=2000-13-45", "--stop-at=2030-12-31T23:59:59"):
             result, _ = run_client(source, dest, flags=[flag],
                                    port=shared_server.port)
             assert result.returncode != 0, f"{flag} should be rejected"