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/test_protocol.c

@@ -291,6 +291,35 @@ static void test_max_alloc_allows_configured_buffer() {
   protocol_session_unbind();
 }
 
+/* max_alloc == 0 is rsync's --max-alloc=0 "no limit": allocations of any size
+ * are permitted. */
+static void test_max_alloc_zero_means_unlimited() {
+  ProtocolSession session;
+  protocol_session_init(&session, -1, -1);
+  protocol_session_set_max_alloc(&session, 0);
+  protocol_session_bind(&session);
+  void* first = protocol_alloc(1024 * 1024);
+  void* second = protocol_alloc(8 * 1024 * 1024);
+  EXPECT_NOT_NULL(first);
+  EXPECT_NOT_NULL(second);
+  free(first);
+  free(second);
+  protocol_session_unbind();
+}
+
+/* A non-positive session io timeout disables the deadline: the getter reports 0
+ * (not the built-in 60 s fallback) so callers know to wait indefinitely. */
+static void test_protocol_get_io_timeout_zero_disables() {
+  ProtocolSession session;
+  protocol_session_init(&session, -1, -1);
+  protocol_session_bind(&session);
+  protocol_session_set_io_timeout(&session, 0);
+  EXPECT_EQ_INT(protocol_get_io_timeout_sec(), 0);
+  protocol_session_set_io_timeout(&session, 45);
+  EXPECT_EQ_INT(protocol_get_io_timeout_sec(), 45);
+  protocol_session_unbind();
+}
+
 static void test_max_alloc_is_bound_in_worker_threads() {
   enum { WORKER_COUNT = 4 };
   ProtocolSession sessions[WORKER_COUNT];
@@ -650,6 +679,8 @@ void test_protocol() {
   test_max_alloc_rejects_single_buffer();
   test_explicit_session_max_alloc_cannot_be_bypassed();
   test_max_alloc_allows_configured_buffer();
+  test_max_alloc_zero_means_unlimited();
+  test_protocol_get_io_timeout_zero_disables();
   test_max_alloc_is_bound_in_worker_threads();
   test_protocol_accounting_is_released_in_worker_threads();
   test_protocol_accounting_reservation_is_atomic();