refactor!: ♻️ change return type of KNN API from []*T to []T

I have changed the return type of `KNN` API from `[]*T` to `[]T`. I made this change to make the APIs of my K-D Tree library consistent with those of existing ones written in Go.

BREAKING CHANGE: With the change of the return type of the `KNN` API from `[]*T` to `[]T` in this commit, any code that uses the `KNN` API will no longer work with future releases of this library created after this commit. Affected codebases must migrate to the updated version of the `KNN` API to be compatible with future releases of this library.

Author: rishitc

kdtree.go

@@ -451,18 +451,18 @@ func nearestNeighbor[T Comparable[T]](d int, v, nn *T, cd int, r *kdNode[T]) *T
 	return nn
 }
 
-func (t *KDTree[T]) KNN(value T, k int) []*T {
+func (t *KDTree[T]) KNN(value T, k int) []T {
 	if t == nil || t.root == nil || t.size < k {
 		return nil
 	}
 
 	pqRes := NewBoundedPriorityQueue[T](k)
 	knn(k, t.dimensions, &value, &pqRes, 0, t.root)
 
-	res := make([]*T, 0, k)
+	res := make([]T, 0, k)
 	for range k {
 		// heap with a preset capacity
-		d := internal.Pop(&pqRes).Data
+		d := *internal.Pop(&pqRes).Data
 		res = append(res, d)
 	}
 

tests/kdtree_2d_test.go

@@ -181,7 +181,7 @@ func Test2DNearestNeighbor5(t *testing.T) {
 	}
 }
 
-func tensor2DSortFunc(a, b *types.Tensor2D) int {
+func tensor2DSortFunc(a, b types.Tensor2D) int {
 	if a[0] != b[0] {
 		return a[0] - b[0]
 	} else {
@@ -206,19 +206,19 @@ func Test2DKNN1(t *testing.T) {
 	tree := kdtree.NewKDTreeWithValues(dimensions2DCount, ps)
 	testTable := map[string]struct {
 		input    input
-		expected []*types.Tensor2D
+		expected []types.Tensor2D
 	}{
 		"Find the 2 closest neighbors to a point that is not in the KD tree.": {
 			input:    input{p: [2]int{25, 25}, k: 2},
-			expected: []*types.Tensor2D{{40, 20}, {10, 25}},
+			expected: []types.Tensor2D{{40, 20}, {10, 25}},
 		},
 		"The closest neighbor to a point that is in the KD tree.": {
 			input:    input{p: [2]int{60, 90}, k: 1},
-			expected: []*types.Tensor2D{{60, 90}},
+			expected: []types.Tensor2D{{60, 90}},
 		},
 		"The three closest neighbors to a point that is in the KD tree.": {
 			input:    input{p: [2]int{70, 70}, k: 3},
-			expected: []*types.Tensor2D{{50, 50}, {60, 90}, {70, 70}},
+			expected: []types.Tensor2D{{50, 50}, {60, 90}, {70, 70}},
 		},
 	}
 	for name, st := range testTable {