#14309 Open summary case without UNSMRY data file as empty reader

A SMSPEC file without a UNSMRY data file is re-read on every request for a summary vector, since RifReaderEclipseSummary::open returns false and no reader is cached. For an ensemble with multiple realizations missing UNSMRY, this is a severe performance problem.

Guard RifReaderEclipseSummary::open so that when no ESMRY, h5 or resdata data file is present, it returns true and creates a valid but empty reader. Skip ESMRY conversion when no UNSMRY is present, and add RifEclipseSummaryTools::hasSummaryDataFiles to detect the missing data file.

ApplicationLibCode/UnitTests/opm-summary-Test.cpp

@@ -418,8 +418,9 @@ TEST( OpmSummaryTests, ReadSmspecWithoutUnsmryEmptyReader )
 
     RifReaderEclipseSummary reader;
 
-    // No summary data file is present, so opening fails, but it must not crash or throw.
-    EXPECT_FALSE( reader.open( filePath, nullptr ) );
+    // No summary data file is present, but opening must succeed and create a valid, but empty, reader.
+    // This ensures the case is opened once and not re-read on every request.
+    EXPECT_TRUE( reader.open( filePath, nullptr ) );
 
     reader.createAndSetAddresses();