Add cell indexes to all diagnostics (#9387)

## Summary

Ensures that any lint rules that include line locations render them as
relative to the cell (and include the cell number) when inside a Jupyter
notebook.

Closes https://github.com/astral-sh/ruff/issues/6672.

## Test Plan

`cargo test`

crates/ruff_source_file/src/lib.rs

@@ -1,5 +1,5 @@
 use std::cmp::Ordering;
-use std::fmt::{Debug, Formatter};
+use std::fmt::{Debug, Display, Formatter};
 use std::sync::Arc;
 
 #[cfg(feature = "serde")]
@@ -253,3 +253,20 @@ impl Debug for SourceLocation {
             .finish()
     }
 }
+
+#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub enum SourceRow {
+    /// A row within a cell in a Jupyter Notebook.
+    Notebook { cell: OneIndexed, line: OneIndexed },
+    /// A row within a source file.
+    SourceFile { line: OneIndexed },
+}
+
+impl Display for SourceRow {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        match self {
+            SourceRow::Notebook { cell, line } => write!(f, "cell {cell}, line {line}"),
+            SourceRow::SourceFile { line } => write!(f, "line {line}"),
+        }
+    }
+}