Implements deeper integration with weave into Templates

[kiranandcode]

This PR proposes an alternative implementation for #493 . Instead of requiring the user to explicitly annotate functions with @weave.op this PR updates the implementation of Template.call to automatically insert @weave.op calls.

@Template.define
def haiku(topic: str) -> str:
  """Generate a haiku about {topic}."""
   raise NotHandled

[eb8680]

weave is a nice library, but it's not obvious why we should bake it into the library as the sole observability solution (especially because it appears to lock you into the wandb platform), or even that it requires library-level support at all. It seems like you could do the same thing with a handler for Template.__apply__ in application code.

[kiranandcode]

Yep, that makes sense. I think I'll update #508 to describe implementing a handler (which also handles the issue I commented regarding tools being hidden).