fix: fix Copy documentation and implementation

Copy should not create slices bigger than original. Fixed that.

Signed-off-by: Dmitriy Matrenichev <dmitry.matrenichev@siderolabs.com>

slices/slices.go

@@ -148,12 +148,16 @@ func Contains[T any](s []T, fn func(T) bool) bool {
 	return IndexFunc(s, fn) >= 0
 }
 
-// Copy returns a slice of V with the last n elements removed.
+// Copy copies first n elements. If n is greater than the length of the slice, it will copy the whole slice.
 func Copy[S ~[]V, V any](s S, n int) S {
 	if s == nil {
 		return nil
 	}
 
+	if n > len(s) {
+		n = len(s)
+	}
+
 	result := make([]V, n)
 	copy(result, s)