tests: the parallel unmerged MTZ table is compared bitwise again

UnmergedMtzTable's columns hold NaN for missing values, and vector<float> == compares NaN unequal to
itself, so the serial-vs-parallel check could fail spuriously. Each column is compared with memcmp,
as the test did before the MtzTable change.

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

tests/WriteReflectionsTest.cpp

@@ -187,8 +187,12 @@ TEST_CASE("Unmerged MTZ: built on several workers, the same rows as on one", "[w
                                                    OutputProvenance{}, 8);
         REQUIRE(serial.columns[0].values.size() > 100000);
         REQUIRE(parallel.columns.size() == serial.columns.size());
-        for (size_t c = 0; c < serial.columns.size(); c++)
-            CHECK(parallel.columns[c].values == serial.columns[c].values);
+        // Bitwise, so the NaN of a missing value compares equal to itself.
+        for (size_t c = 0; c < serial.columns.size(); c++) {
+            REQUIRE(parallel.columns[c].values.size() == serial.columns[c].values.size());
+            CHECK(std::memcmp(parallel.columns[c].values.data(), serial.columns[c].values.data(),
+                              serial.columns[c].values.size() * sizeof(float)) == 0);
+        }
         REQUIRE(parallel.batches.size() == serial.batches.size());
         CHECK(parallel.batches.front().number == serial.batches.front().number);
         CHECK(parallel.batches.back().number == serial.batches.back().number);