[Rust] upgrade to 1.81

[ebmifa]

Fixing

~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; error[E0658]
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; : use of unstable library feature 'result_option_inspect'
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; -->
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; /usr/local/cargo/git/checkouts/sui-6ac459c53b1b685a/e3e5ac7/external-crates/move/crates/move-compiler/src/parser/syntax.rs:3191:10
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; |
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; 3191
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; |
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; .inspect_err(|diag| ***
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; |
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; ^^^^^^^^^^^
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; |
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; =
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; note
 ~  docker:index:Image gas-station-image updating (549s) [diff: ~build]; : see issue #91345 <https://github.com/rust-lang/rust/issues/91345> for more information

See MystenLabs/sui#19529