Document public types in nu-protocol (#12906)

- **Doc-comment public `nu-protocol` modules**
- **Doccomment argument/signature/call stuff**
- **Doccomment cell path types**
- **Doccomment expression stuff**
- **Doccomment import patterns**
- **Doccomment pattern matching AST nodes**

crates/nu-protocol/src/errors/cli_error.rs

@@ -1,3 +1,6 @@
+//! This module manages the step of turning error types into printed error messages
+//!
+//! Relies on the `miette` crate for pretty layout
 use crate::{
     engine::{EngineState, StateWorkingSet},
     ErrorStyle,