Core: hot reload components from installed apworld (#3480)

* Core: hot reload components from installed apworld

* address PR reviews

`Launcher` widget members default to `None` so they can be defined in `build`

`Launcher._refresh_components` is not wrapped

loaded world goes into `world_sources` so we can check if it's already loaded.
(`WorldSource` can be ordered now without trying to compare `None` and `float`)
(don't load empty directories so we don't detect them as worlds)

* clarify that the installation is successful

typings/schema/__init__.pyi

@@ -0,0 +1,17 @@
+from typing import Any, Callable
+
+
+class And:
+    def __init__(self, __type: type, __func: Callable[[Any], bool]) -> None: ...
+
+
+class Or:
+    def __init__(self, *args: object) -> None: ...
+
+
+class Schema:
+    def __init__(self, __x: object) -> None: ...
+
+
+class Optional(Schema):
+    ...