Profile unit tests

I want to use puffin to profile my tests but am having problems getting the viewer to catch the single frame it produces. It might be related to #85. I've had it somewhat working but that was a few versions of puffin ago.

My tests looks like this right now and I would be happy if something similar worked:
```rs
#[test]
fn test_ik_solver_neutral() -> hotham::anyhow::Result<()> {
let _ = start_puffin_server();
puffin::profile_function!();
test_ik_solver(
include_str!("../../test_data/inverse_kinematics_snapshot_2023-04-12_22.23.47.json"),
None,
)
}
```

The function `start_puffin_server` is something I wrote to create a `puffin_http::Server` and keep it alive until the test is done. It calls `puffin::GlobalProfiler::lock().new_frame();` when created and dropped. I would like to use something like `puffin::profile_unit_test!();` instead. Writing to disk is an option but I would prefer if I can keep the viewer running and update automatically as I change the code and run the test again.

Start by tracing the test entry points in the example: start_puffin_server, puffin::GlobalProfiler::lock().new_frame(), puffin::profile_function!(), and puffin_http::Server. Reproduce the single-frame test with the viewer running, then determine what a puffin::profile_unit_test!() API would need to do so rerunning the test updates the viewer automatically.

Written by the indexing model from the issue text.