Work out Tracing and timing

[Janekdererste]

We want timing information on our application to create nice images. This requires log files in CSV format, as reading in JSON in R is pretty slow, once the log files reach a certain size. It seems like CSV files are parsed much quicker. This is not supported by the tracing crate out of the box, I think.

I would prefer the tracing crate, over a custom solution, since we are using this dependency anyway. We can time methods using the #[instrument] directive and the framework takes care of most of the other stuff.

After tinkering around with the tracing crate, I think we should go for the following solution:

• Use the tracing crate for timing the application
• Either implement a custom formatter, which requires a custom writer, as well as a custom visitor, to properly write the data we need. This is not particularly handy, because it requires a lot of infrastructure
• My preferred solution is to directly implement the Layer trait, which gives full control over state management and filtering. This disables us from using all the infrastructure the tracing_subscriber crate has for writing and formatting logs, but it is complicated to use anyway. I think it is easier to do it this way.

[paulheinr]

@Janekdererste did it 🚀