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/lexer.rs

@@ -290,7 +290,7 @@ impl<'src> Lexer<'src> {
                         LexicalErrorType::IndentationError,
                         self.token_range(),
                     )));
-                };
+                }
 
                 // The lexer might've eaten some whitespaces to calculate the `indentation`. For
                 // example:
@@ -1071,7 +1071,7 @@ impl<'src> Lexer<'src> {
         if first_digit_or_dot != '.' {
             number.push(first_digit_or_dot);
             self.radix_run(&mut number, Radix::Decimal);
-        };
+        }
 
         let is_float = if first_digit_or_dot == '.' || self.cursor.eat_char('.') {
             number.push('.');