[red-knot] Merge Markdown code blocks inside a single section (#15950)

## Summary

Allow for literate style in Markdown tests and merge multiple (unnamed)
code blocks into a single embedded file.

closes #15941

## Test Plan

- Interactively made sure that error-lines were reported correctly in
  multi-snippet sections.

crates/ruff_python_ast/src/lib.rs

@@ -69,7 +69,7 @@ pub enum TomlSourceType {
     Unrecognized,
 }
 
-#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub enum PySourceType {
     /// The source is a Python file (`.py`).