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_python_parser/src/parser/statement.rs

@@ -1,5 +1,5 @@
 use compact_str::CompactString;
-use std::fmt::Display;
+use std::fmt::{Display, Write};
 
 use rustc_hash::{FxBuildHasher, FxHashSet};
 
@@ -1028,7 +1028,7 @@ impl<'src> Parser<'src> {
                         ..
                     }) = &**slice
                     {
-                        buffer.push_str(&format!("{integer}"));
+                        let _ = write!(buffer, "{integer}");
                     } else {
                         parser.add_error(
                             ParseErrorType::OtherError(