udpate rust toolchain to rust 1.81.0 (#14473)

# Description

With the release of rust 1.83.0 it's time to update to rust 1.81.0.

crates/nu-parser/src/parser.rs

@@ -1,3 +1,5 @@
+#![allow(clippy::byte_char_slices)]
+
 use crate::{
     lex::{is_assignment_operator, lex, lex_n_tokens, lex_signature, LexState},
     lite_parser::{lite_parse, LiteCommand, LitePipeline, LiteRedirection, LiteRedirectionTarget},