LuckyPennySoftware/MediatR ? reverse-engineered prompt

Build me a simple C# library for my .NET projects that helps decouple my code. The main idea is to create an in-process messaging system. Instead of having my API controllers or services call business logic directly, I want to send a "request" object and have a dedicated handler class process it and return a response. This should work for both queries that return data and commands that perform an action.

It should also support "fire-and-forget" style notifications, where I can publish an event and have multiple different handlers react to it independently. Everything should be asynchronous and work well with async/await. Make it easy to integrate into an ASP.NET Core application, so I can just add it to my services and it will automatically discover all my request and notification handlers from my assemblies. It should be lightweight with no other dependencies.