Currently, if you print a Message object of a list of Messages it just shows the memory address of the class, which is lame.

[<torchtune.data._messages.Message at 0x7fc0e5f6cd30>,
 <torchtune.data._messages.Message at 0x7fc0e67f2470>]

We should implement a proper __str__ method to make the output legible. Ideally, something like:

Message(role="user", content="Hello world!")