refactor(jupyter): use runtimelib for Jupyter structures and directory paths

[rgbkrk]

Posting this up for now before I hack with @bartlomieju next week.

This brings in runtimelib to use:

Fully typed structs for Jupyter Messages

let msg = connection.read().await?;

self
  .send_iopub(
    messaging::Status {
      execution_state: "busy".to_string(),
    }
    .as_child_of(msg),
  )
  .await?;

Jupyter paths

Jupyter paths are implemented in Rust, allowing the Deno kernel to be installed completely via Deno without a requirement on Python or Jupyter. Deno users will be able to install and use the kernel with just VS Code or other editors that support Jupyter.

pub fn status() -> Result<(), AnyError> {
  let user_data_dir = user_data_dir()?;

  let kernel_spec_dir_path = user_data_dir.join("kernels").join("deno");
  let kernel_spec_path = kernel_spec_dir_path.join("kernel.json");

  if kernel_spec_path.exists() {
    log::info!("✅ Deno kernel already installed");
    Ok(())
  } else {
    log::warn!("ℹ️ Deno kernel is not yet installed, run `deno jupyter --install` to set it up");
    Ok(())
  }
}

I tested this out across all the notebooks in https://github.com/rgbkrk/denotebooks, which was also a great chance for me to switch them all to jsr: wherever possible. Update: anywidget is also working (cc @manzt)!