Now that you have an overview of enums and it's possible variants, let's have a more complex example.

In this challenge, you will create an Animal enum that demonstrates all three types of variants.

Create an enum Animal with the following variants:

1. Unit Struct Variant:

   • Dog — represents a generic dog.

2. Tuple Struct Variant:

   • Cat(String) — represents a cat, where the String contains the cat's name.

3. Named Field Struct Variant:

   • Bird { species: String, can_fly: bool } — represents a bird with its species and whether it can fly.

Write a function describe_animal that takes a reference to an Animal and returns a String description based on the variant:

• For Dog, return "A friendly dog.".
• For Cat(name), return "A cat named {name}.".
• For Bird { species, can_fly }, return:
  • "A {species} that can fly." if can_fly is true.
  • "A {species} that cannot fly." if can_fly is false.