Validation for lightweight components

[mrchtr]

Adding validation to the PythonComponent.

• change BaseComponents methods to abstractmethods
• validate that all abstractmethods were implemented in the PythonComponent
• validate that the function interface is the same as in the BaseComponents

Fix #783

[GeorgesLorre]

One thing I noticed while writing tests:

@lightweight_component()
    class Foo(DaskLoadComponent):
        def load(self) -> str:
            return ["bar"]works

but

@lightweight_component
    class Foo(DaskLoadComponent):
        def load(self) -> str:
            return ["bar"]

does not

Notice the () on the decorator. It might be nice to support both or at least throw a clear error.

[mrchtr]

One thing I noticed while writing tests:

@lightweight_component()
    class Foo(DaskLoadComponent):
        def load(self) -> str:
            return ["bar"]works

but

@lightweight_component
    class Foo(DaskLoadComponent):
        def load(self) -> str:
            return ["bar"]

does not

Notice the () on the decorator. It might be nice to support both or at least throw a clear error.

Added the support for both variants. When we call the decorator without parentheses the default values of the Image will be used.

[GeorgesLorre]

Nice ! We can still expand once we discover more cases.