docs: clarify Empty returns zero value

https://go.dev/ref/spec#The_zero_value does not define "empty value". It informally mentions "empty value", meaning (non-nil && 0-length) slice or map.

> Note that the zero value for a slice or map type is not the same as an initialized but empty value of the same type.

type_manipulation.go

@@ -106,7 +106,7 @@ func FromAnySlice[T any](in []any) (out []T, ok bool) {
 	return result, true
 }
 
-// Empty returns an empty value.
+// Empty returns the zero value (https://go.dev/ref/spec#The_zero_value).
 func Empty[T any]() T {
 	var zero T
 	return zero

type_manipulation_test.go

@@ -180,6 +180,8 @@ func TestEmpty(t *testing.T) {
 	is.Empty(Empty[int64]())
 	is.Empty(Empty[test]())
 	is.Empty(Empty[chan string]())
+	is.Nil(Empty[[]int]())
+	is.Nil(Empty[map[string]int]())
 }
 
 func TestIsEmpty(t *testing.T) {