Type-safe context

[johannescpk]

Currently context registration / consumption isn't type-safe and can fail at runtime. Axum somehow figured out how to make it type-safe. Didn't have the chance yet to look into the details, but thought I leave this here as a reminder / hint:

https://tokio.rs/blog/2022-08-whats-new-in-axum-0-6-0-rc1