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_formatter/src/lib.rs

@@ -7,10 +7,10 @@
 //!
 //! * [`Format`]: Implemented by objects that can be formatted.
 //! * [`FormatRule`]: Rule that knows how to format an object of another type. Useful in the situation where
-//!    it's necessary to implement [Format] on an object from another crate. This module defines the
-//!    [`FormatRefWithRule`] and [`FormatOwnedWithRule`] structs to pass an item with its corresponding rule.
+//!   it's necessary to implement [Format] on an object from another crate. This module defines the
+//!   [`FormatRefWithRule`] and [`FormatOwnedWithRule`] structs to pass an item with its corresponding rule.
 //! * [`FormatWithRule`] implemented by objects that know how to format another type. Useful for implementing
-//!    some reusable formatting logic inside of this module if the type itself doesn't implement [Format]
+//!   some reusable formatting logic inside of this module if the type itself doesn't implement [Format]
 //!
 //! ## Formatting Macros
 //!