Refactor Day04 and Day09 to rename methods and variables for improved clarity and update Day09 tests with additional input file and test case

AoC_2025/Day04.cs

@@ -55,13 +55,12 @@ public class Day04 : IPuzzleSolver<long>
     private HashSet<Coordinate> GetRollCoordinates(IEnumerable<string> paperrollGrid)
     {
         var coordinates = paperrollGrid
-            .Index()
-            .SelectMany(indexedLine => GetCoordinates(indexedLine.Item, indexedLine.Index))
+            .SelectMany((line, xIndex) => GetRollCoordinates(line, xIndex))
             .ToHashSet();
         return coordinates;
     }
 
-    private IEnumerable<Coordinate> GetCoordinates(string gridLine, int xIndex)
+    private IEnumerable<Coordinate> GetRollCoordinates(string gridLine, int xIndex)
     {
         var indexedCharacters = gridLine.Index();
         var validRolls = indexedCharacters.Where(tuple => tuple.Item == '@');

AoC_2025/Day09.cs

@@ -64,7 +64,8 @@ public class Day09 : IPuzzleSolver<long>
 
     private bool IsRectangleInsideBorders(CoordinatePair[] borders, CoordinatePair rectangle)
     {
-        return !borders.Any(border => RectangleCrossesBorder(rectangle, border));
+        var bordersCrossed = borders.Any(border => RectangleCrossesBorder(rectangle, border));
+        return !bordersCrossed;
     }
 
     private CoordinatePair AsPair(Coordinate a, Coordinate b)