Extract Combinations method to AdventOfCode.Extensions and refactor usages to improve modularity and reduce duplication

AoC_2025/Day09.cs

@@ -4,6 +4,7 @@ using System.Data.Common;
 using System.IO;
 using System.Linq;
 using AdvenOfCode.Contracts;
+using AdventOfCode.Extensions;
 using Coordinate = (long x, long y);
 using CoordinatePair = (long minX, long minY, long maxX, long maxY);
 
@@ -54,7 +55,7 @@ public class Day09 : IPuzzleSolver<long>
 
     private IEnumerable<CoordinatePair> GetAllPossibleRectanglesAsPairs(Coordinate[] redTiles)
     {
-        return Combinations(redTiles).Select(x => AsPair(x.a, x.b));
+        return redTiles.Combinations(2).Select(x => AsPair(x[0], x[1]));
     }
 
     private CoordinatePair[] GetBordersAsPairs(Coordinate[] redTiles)
@@ -84,17 +85,6 @@ public class Day09 : IPuzzleSolver<long>
         return (Math.Abs(tileA.x - tileB.x) + 1) * (Math.Abs(tileA.y - tileB.y) + 1);
     }
 
-    private IEnumerable<(TValue a, TValue b)> Combinations<TValue>(IEnumerable<TValue> values)
-    {
-        var enumeratedValues = values.Index().ToArray();
-        var pairs = 
-            from a in enumeratedValues
-            from b in enumeratedValues
-            where a.Index < b.Index
-            select (a.Item, b.Item);
-        return pairs;
-    }
-
     private IEnumerable<(Coordinate a, Coordinate b)> GetBorders(Coordinate[] tiles)
     {
         return tiles.Zip([..tiles[1..], tiles[0]], (a, b) => (a, b));