possible violation of spec in step.add_extension

[mimir-d]

Step extension api is defined as following

async fn add_extension<S: serde::Serialize>(&self, name: &str, any: S)

This means it will accept any Serialize, including primitive types (eg. string, u32, etc). Per the spec, this is incorrect, and we should only accept full objects.

This issue is for tracking and ideas how to fix this. At the current moment, I'm not aware of a way to specify a trait bound only for structs.

cc @njordr