## Summary
This PR updates the `FileCache` to include an optional `NotebookIndex`
to support caching for Jupyter Notebooks.
We only require the index to compute the diagnostics and thus we don't
really need to store the entire `Notebook` on the `Diagnostics` struct.
This means we only need the index to be stored in the cache to
reconstruct the `Diagnostics`.
## Test Plan
Update an existing test case to run over the fixtures under
`ruff_notebook` crate where there are multiple Jupyter Notebook.
Locally, the following commands were run in order:
1. Remove the cache: `rm -rf .ruff_cache`
2. Run without cache: `cargo run --bin ruff -- check --isolated
crates/ruff_notebook/resources/test/fixtures/jupyter/unused_variable.ipynb
--no-cache`
3. Run with cache: `cargo run --bin ruff -- check --isolated
crates/ruff_notebook/resources/test/fixtures/jupyter/unused_variable.ipynb`
4. Check whether the `.ruff_cache` directory was created or not
5. Run with cache again and verify: `cargo run --bin ruff -- check
--isolated
crates/ruff_notebook/resources/test/fixtures/jupyter/unused_variable.ipynb`
## Benchmarks
https://github.com/astral-sh/ruff/pull/6863#issuecomment-1715675186fixes: #6671
## 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`
