Base `Operation` constructor should call `infer_annotations` for all annotations in a signature

[eb8680]

Now that we're adding more effectful.ops.types.Annotation subtypes to control Operation behavior (see e.g. #222 #171 #448 #447), we should be more precise and explicit about the specification of Annotation.

Currently the only method on the abstract base class Annotation is infer_annotations, which takes an inspect.Signature and returns another Signature which may have had Annotations validated and added/removed/edited. This should be run in Operation.__init__, or if there are forward references (#450) perhaps the first time the __signature__ property is accessed (#451).

infer_annotations should also be idempotent and should not affect either the underlying un-annotated type or other Annotations that are not instances. This can just be enforced implicitly with documentation and unit tests for now.