Enable auto-completion

Hi @timtreis,

I never had access to code auto-completion using spatialdata-plot. I guess it's not specific to me, but likely related to the way _register_accessor is used, correct?

I guess you already investigated why the auto-completion doesn't work, so you may already have insights regarding this. Do you think it's something that could be potentially fixed, or is it not planned at all?

该 issue 将 _register_accessor 确定为疑似入口点；首先跟踪它如何注册 spatialdata-plot accessor，以及它的成员如何暴露给 Python 补全工具。查找现有的 accessor 相关测试或验证。完成此项需要约定好的补全行为和一个回归测试，但该 issue 未指定文件，也未定义预期的 API。