fix: Rewrite Type Handling

[natemort]

Move type handling logic from activity.py to fn_signature.py, providing utilities for understanding a functions parameters and converting calls/payloads to match the function's signature.

Use this new logic in Workflows, to support any number of typed parameters.

Rewrite the Activity decorators to be fully type-safe. Introduce @activity.method and @activity.impl to satisfy type safety while allowing for interface types or classes that contain activities. These definitions are quite complicated for a few reasons:

• We allow both activity.defn and activity.defn(), which means we need to handle both being or returning a decorator
• We allow both async and non-async activity definitions, which we need to handle the result of differently (Awaitable[T] vs T).
  • If a function returns Awaitable[T] we don't want to return Awaitable[Awaitable[T]].
• We support both standalone functions and methods.
  • When a method is accessed the __get__ special method is invoked, which returns the function with the self parameter already filled.
  • If it's accessed via ClassName.foo then __get__ is invoked with None, and the returned function doesn't have the filled self parameter.
• To support overriding an activity definition (such as making an interface that has the definitions), we need the subclass to have a property that's an identical ActivityDefinition. Otherwise it's not a valid subclass.
  • The activity.impl decorator was added to support this. Maybe it makes more sense to call it override.

Fix type-safety for Workflows. This only addresses the annotations and doesn't provide a type-safe invocation mechanism like what is supported with Activities. That will be explored in a future diff.

What changed?

• Refactor function inspection to share between Workflows and Activities
• Rewrite activity typing to be fully type-safe.
  • Pycharm is broadly confused by it, but mypy approves.
• Use new typing support to handle Workflows with parameters.

Why?

• Fix type-safety for Workflows.
• Support multiple parameters in Workflows.

How did you test it?

• Integration and unit tests

Potential risks

• This is a breaking change.

Release notes

Documentation Changes

[natemort]

Reviewed offline

[shijiesheng]

no need to specify typing in the implementation since typing is already hinted in the overload.

[natemort]

The implementation references the various type parameters unfortunately :( .

[shijiesheng]

why does ActivityDefinition needs to have call method? I think this is where introduced all the sync/async branches.

[natemort]

Without __call__ we'd be transforming their functions into something that isn't Callable. They'd no longer be able to directly invoke any decorated functions