Encourage synchronous activities more

Describe the solution you'd like

• Rename hello/hello_activity.py to hello/hello_activity_async.py (and README refs and what not)
• Rename hello/hello_activity_threaded.py to hello/hello_activity.py (and README refs and what not)
• Consider changing other samples to use def instead of async def where it makes sense

首先检查 hello/hello_activity.py、hello/hello_activity_threaded.py 以及 README 中对这些示例的引用。按要求重命名文件并更新引用，然后检查其他示例，寻找适合使用 synchronous def 的情况。当名称和 README 链接保持一致，且选定的示例使用预期的风格时，即表示完成。