jfjoch_writer writes rugnux's .mtz, _maps.mtz and _model.cif from the END blocks

New gemmi-only library JFJochRugnuxFiles (writer/), linked by JFJochWriter, so
the writer needs no analysis library and builds with JFJOCH_WRITER_ONLY:
- WriteMergedMtz / WriteMapCoefficientsMtz / PlacedModelStructure make the
  files from the structured blocks; WriteRugnuxResultFiles writes whichever
  blocks END carries beside the master, each under a temporary name and renamed
  into place, an existing file replaced only when the run's overwrite is set.
  A file that fails costs only itself (logged), not the run.
- FillRugnuxResultBlocks reads the blocks back from the files rugnux wrote at
  a prefix (p.mtz, p_maps.mtz, p_model.cif), for the broker to fill END.

WriteMtzReflections now goes through WriteMergedMtz (MergedReflectionsForWriter
builds the block); its output is byte-identical to before, checked by md5 on a
synthetic set in both the Friedel-merged and the anomalous layout.

StreamWriter writes the files after the master and before the END ACK, so the
ACK means they are in place; END receipt and each rename are logged at INFO
with the wall-clock time, for last-frame-to-files latency. The broker's direct
HDF5 pusher writes them too.

Test: rugnux's three files -> blocks -> CBOR -> writer reproduces all of them
(and _model.pdb) byte for byte; a ~25k-reflection END is 2.7 MB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

image_pusher/HDF5FilePusher.cpp

@@ -66,6 +66,7 @@ bool HDF5FilePusher::EndDataCollection(const EndMessage &message) {
         if (!writer)
             throw JFJochException(JFJochExceptionCategory::WrongDAQState, "Image pusher not ready for writing images");
         writer->WriteHDF5(message);
+        writer->WriteResultFiles(message, logger);
         writer->Finalize();
     } catch (...) {
         writer.reset();