Make `func.delay` typed when decorating `func` with `@tiger.task`

[neob91-close]

We're currently assigning delay as the attribute of func here, which results in the type of func.delay being Any.

To improve type safety, we should instead:

• define a new class (called TaskDefinition?) with proper type annotations for delay, __call__ (etc.)
• wrap func in an instance of that new class (wrapped = TaskDefinition(self, func))

[neob91-close]

This was reverted.