Error when configuring components with values inherited from factories

[AdamHillier]

The following fails:

    @factory
    class IntFactory:
        def build(self) -> int:
            return 5

    @component
    class Child:
        x: int = ComponentField()

    @component
    class Parent:
        child: Child = ComponentField(Child)
        x: int = ComponentField(IntFactory)

    p = Parent()
    configure(p, {})
    assert p.x == 5
    assert p.child.x == 5

with error AttributeError: 'int' object has no attribute '__component_configured__'.

This happens because configure() tries to recursively configure p.child.x, as it is a ComponentField (shadowing p.x, which is a ComponentField). But p.child.x resolves to an integer. We can solve this by checking that the thing we try and recursively configure is a component instance (this will not break type-checking, which happens separately).