Avoid B015,B018 for last expression in a cell (#8815)

## Summary

This PR updates `B015` and `B018` to ignore last top-level expressions
in each cell of a Jupyter Notebook.

Part of #8669

## Test Plan

Add test cases for both rules and update the snapshots.

crates/ruff_linter/src/linter.rs

@@ -163,6 +163,7 @@ pub fn check_path(
                         path,
                         package,
                         source_type,
+                        cell_offsets,
                     ));
                 }
                 if use_imports {