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

<!--
Thank you for contributing to Ruff! To help us out with reviewing,
please consider the following:

- Does this pull request include a summary of the change? (See below.)
- Does this pull request include a descriptive title?
- Does this pull request include references to any relevant issues?
-->

## 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_python_formatter/src/verbatim.rs

@@ -478,7 +478,7 @@ enum SuppressionComments<'a> {
         /// Any following `fmt: off` comment if any.
         /// * `None`: The suppression ends here (for good)
         /// * `Some`: A `fmt: off`..`fmt: on` .. `fmt: off` sequence. The suppression continues after
-        ///     the `fmt: off` comment.
+        ///   the `fmt: off` comment.
         format_off_comment: Option<&'a SourceComment>,
     },