Fix integer truncation in CatchBeatmapProcessor time delta calculation

Changed `timeDiff` calculation from `int` to `double` in `applyHardRockOffset` to prevent precision loss which was affecting randomization and offset application.
Updated expected values for `CatchBeatmapConversionTest` case `1431386` as the fix alters Hard Rock object positions.
Added `CatchBeatmapProcessorTest` to verify the fix.
Addressed code style issues (license header, object initializer).

Co-authored-by: winnerspiros <1675249+winnerspiros@users.noreply.github.com>

Author: google-labs-jules[bot]

osu.Game.Rulesets.Catch.Tests/CatchBeatmapProcessorTest.cs

@@ -39,8 +39,10 @@ public void TestHardRockOffsetDoublePrecision()
                 }
             };
 
-            var processor = new CatchBeatmapProcessor(beatmap);
-            processor.HardRockOffsets = true;
+            var processor = new CatchBeatmapProcessor(beatmap)
+            {
+                HardRockOffsets = true
+            };
 
             processor.ApplyPositionOffsets(beatmap);