Common base class

Currently both DynamicCore and StaticCore extend HybridCore. This is a bit strange inheritance hierarchy in general, but it's especially stupid to check does a library extend any of these by using isinstance(library, HybridCore). It would be better to have a common base class named LibraryCore or RobotLibraryCore that all concrete lib cores extend. It would allow using isinstance(library, RobotLibraryCore).

Until this common base class is implemented, it's probably best to use isinstance(library, (HybridCore, DynamicCore, StaticCore)) with any generic code. That's both more explicit than just using isinstance(library, HybridCore) and also works if and when other cores don't anymore extend HybridCore.

首先定位 HybridCore、DynamicCore 和 StaticCore 的定义及使用位置。审查共享的 LibraryCore 或 RobotLibraryCore 会如何影响继承和通用的 isinstance 检查；完成的标准是具体的 core 共享新的基类，而不依赖 HybridCore 作为公共类型。