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.

src/shared/config.h

@@ -314,12 +314,13 @@ typedef struct Config {
   char* tls_cert;
   char* tls_key;
   char* tls_ca;
-  /* --timeout: per-message I/O deadline in seconds.  0 (the default/unset
-   * sentinel) leaves the transport's built-in 30 s socket timeout and the
-   * protocol's built-in 60 s per-message deadline in place; a positive value
-   * overrides both.  See protocol_session_set_io_timeout. */
+  /* --timeout: per-message I/O deadline in seconds.  0 (rsync's default)
+   * disables the deadline entirely on both the socket layer and the protocol
+   * layer; a positive value sets it.  See protocol_session_set_io_timeout and
+   * tcp_set_timeouts. */
   int timeout;
-  /* --contimeout: connect()/accept timeout, transport layer only. */
+  /* --contimeout: connect()/accept timeout in seconds (rsync's default 60);
+   * 0 disables it.  Transport layer only. */
   int contimeout;
   bool quiet;
   bool stats;