Tests: the stills rocking width - the window at a reflection's resolution, _process.h5 round trip

StillsPartialityRefine_MeasureRunWidth_WindowAtReflectionResolution, JFJochReader_StillsRunWidth.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015CeEGgpKdfkCTJb3YNMJcu
(cherry picked from commit dafb8d1bf996d1000741eecf019aee780dd91ebe)

tests/JFJochReaderTest.cpp

@@ -2776,6 +2776,61 @@ TEST_CASE("JFJochReader_ReadReflections_Reindex", "[HDF5][Full]") {
     REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
 }
 
+// A stills run's rocking curve (the one its partialities were computed from) goes to the master file and
+// comes back whole, so --mode scale merges with it instead of measuring another; a file without it reads
+// back without one.
+TEST_CASE("JFJochReader_StillsRunWidth", "[HDF5][Full]") {
+    for (const bool with_width: {true, false}) {
+        DiffractionExperiment x(DetJF(1));
+        x.FilePrefix("read_stills_run_width")
+         .ImagesPerTrigger(1)
+         .ImagesPerFile(1)
+         .OverwriteExistingFiles(true)
+         .BitDepthImage(16)
+         .PixelSigned(true)
+         .SetFileWriterFormat(FileWriterFormat::NXmxVDS)
+         .Compression(CompressionAlgorithm::NO_COMPRESSION);
+
+        const StillsRunWidth w{.gamma0 = 1.25e-4, .gamma_e = 6.1e-4, .bandwidth_sigma = 1.7e-3,
+                               .radial_scale = 1.0 + 3.3e-4,
+                               .table_dstar = {0.1, 0.25, 0.4}, .table_s = {1.1e-4, 1.4e-4, 2.2e-4}};
+        RegisterHDF5Filter();
+        {
+            StartMessage start_message;
+            x.FillMessage(start_message);
+            FileWriter writer(start_message);
+            std::vector<int16_t> image(x.GetPixelsNum(), 0);
+            DataMessage message{};
+            message.image = CompressedImage(image, x.GetXPixelsNum(), x.GetYPixelsNum());
+            message.number = 0;
+            REQUIRE_NOTHROW(writer.WriteHDF5(message));
+            EndMessage end_message;
+            end_message.max_image_number = 1;
+            if (with_width)
+                end_message.stills_run_width = w;
+            writer.WriteHDF5(end_message);
+            writer.Finalize();
+        }
+        {
+            JFJochHDF5Reader reader;
+            REQUIRE_NOTHROW(reader.ReadFile("read_stills_run_width_master.h5"));
+            const auto &got = reader.GetDataset()->stills_run_width;
+            REQUIRE(got.has_value() == with_width);
+            if (with_width) {
+                CHECK(got->gamma0 == w.gamma0);
+                CHECK(got->gamma_e == w.gamma_e);
+                CHECK(got->bandwidth_sigma == w.bandwidth_sigma);
+                CHECK(got->radial_scale == w.radial_scale);
+                CHECK(got->table_dstar == w.table_dstar);
+                CHECK(got->table_s == w.table_s);
+            }
+        }
+        remove("read_stills_run_width_master.h5");
+        remove("read_stills_run_width_data_000001.h5");
+    }
+    REQUIRE(H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_ALL) == 0);
+}
+
 static std::vector<SpotToSave> MakeTestSpots(int i) {
     return {
         SpotToSave{