Upgrade to Rust 1.86 and bump MSRV to 1.84 (#17171)

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## Summary

I decided to disable the new
[`needless_continue`](https://rust-lang.github.io/rust-clippy/master/index.html#needless_continue)
rule because I often found the explicit `continue` more readable over an
empty block or having to invert the condition of an other branch.


## Test Plan

`cargo test`

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ruff_notebook/src/notebook.rs

@@ -5,10 +5,10 @@ use serde_json::error::Category;
 use std::cmp::Ordering;
 use std::collections::HashSet;
 use std::fs::File;
+use std::io;
 use std::io::{BufReader, Cursor, Read, Seek, SeekFrom, Write};
 use std::path::Path;
 use std::sync::OnceLock;
-use std::{io, iter};
 use thiserror::Error;
 
 use ruff_diagnostics::{SourceMap, SourceMarker};
@@ -340,9 +340,10 @@ impl Notebook {
                     }
                 }
             };
-            row_to_cell.extend(
-                iter::repeat(OneIndexed::from_zero_indexed(cell_index as usize)).take(line_count),
-            );
+            row_to_cell.extend(std::iter::repeat_n(
+                OneIndexed::from_zero_indexed(cell_index as usize),
+                line_count,
+            ));
             row_to_row_in_cell.extend((0..line_count).map(OneIndexed::from_zero_indexed));
         }