metadata times: -U/--atimes, -N/--crtimes, --open-noatime, -O/-J

Capture+transmit source atime (pre-read stat; O_NOATIME sender guard) and birth
time (statx STATX_BTIME); receiver restores atime with mtime (crtime not settable
portably -> transmitted, explicitly not applied). --open-noatime is client-only.
-O/-J documented as accepted no-ops (FastSync never preserves dir/symlink times).
Wire: metadata frame gains atime/crtime val+sec+nsec; PROTOCOL_VERSION
2.11.0->2.12.0. Review fixes: gate atime capture to Linux (no epoch clobber on
non-Linux), close fd on fdopen failure, honest -O/-J status (Compat no-op).

src/client/client_send.c

@@ -82,6 +82,8 @@ static bool prepare_scanner(const Config* config, int num_threads, PreparedScann
 
   ScannerOptions* options = &out->options;
   options->use_metadata = config->use_metadata;
+  options->preserve_atimes = config->preserve_atimes;
+  options->preserve_crtimes = config->preserve_crtimes;
   options->chunk_size = config->chunk_size;
   options->exclude_patterns = config->exclude_patterns;
   options->exclude_count = config->exclude_count;