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_codegen/src/generator.rs

@@ -1170,7 +1170,7 @@ impl<'a> Generator<'a> {
                 } else {
                     self.unparse_expr(value, precedence::MAX);
                     self.p(".");
-                };
+                }
                 self.p_id(attr);
             }
             Expr::Subscript(ast::ExprSubscript { value, slice, .. }) => {