Create ruff_notebook crate (#7039)

## Summary

This PR moves `ruff/jupyter` into its own `ruff_notebook` crate. Beyond
the move itself, there were a few challenges:

1. `ruff_notebook` relies on the source map abstraction. I've moved the
source map into `ruff_diagnostics`, since it doesn't have any
dependencies on its own and is used alongside diagnostics.
2. `ruff_notebook` has a couple tests for end-to-end linting and
autofixing. I had to leave these tests in `ruff` itself.
3. We had code in `ruff/jupyter` that relied on Python lexing, in order
to provide a more targeted error message in the event that a user saves
a `.py` file with a `.ipynb` extension. I removed this in order to avoid
a dependency on the parser, it felt like it wasn't worth retaining just
for that dependency.

## Test Plan

`cargo test`

crates/ruff/src/message/mod.rs

@@ -14,12 +14,11 @@ pub use json_lines::JsonLinesEmitter;
 pub use junit::JunitEmitter;
 pub use pylint::PylintEmitter;
 use ruff_diagnostics::{Diagnostic, DiagnosticKind, Fix};
+use ruff_notebook::Notebook;
 use ruff_source_file::{SourceFile, SourceLocation};
 use ruff_text_size::{Ranged, TextRange, TextSize};
 pub use text::TextEmitter;
 
-use crate::jupyter::Notebook;
-
 mod azure;
 mod diff;
 mod github;