Instrument the codebase more

[nagisa]

We should instrument the runtime internals and distinct stages so that it is easier to tell what the operation looks like down to the details.

Goal: It should be possible to enable the trace level, attach some visualizer and grasp the structure and operation of the codebase entirely by looking at the output.

Technologies: https://github.com/rust-lang/measureme or tracing, or a combination of both (I hacked on a tracing-measureme crate a long time ago, but never published one).