refactor(core): remove #![feature(let_else)]

The `let_else` feature was stabilized by [rust-lang/rust#93628][1].

[1]: rust-lang/rust#93628

Author: yvt

examples/basic_wio_terminal/src/main.rs

@@ -4,7 +4,6 @@
 #![feature(naked_functions)]
 #![feature(const_mut_refs)]
 #![feature(asm_const)]
-#![feature(let_else)]
 #![deny(unsafe_op_in_unsafe_fn)]
 #![no_std]
 #![no_main]

src/r3_core/src/lib.rs

@@ -46,7 +46,6 @@
 #![feature(never_type)] // `!`
 #![feature(const_try)]
 #![feature(fn_traits)] // `impl FnOnce`
-#![feature(let_else)]
 #![feature(doc_cfg)] // `#[doc(cfg(...))]`
 #![cfg_attr(test, feature(is_sorted))]
 #![deny(unsafe_op_in_unsafe_fn)]

src/r3_core/src/utils/alloc.rs

@@ -48,7 +48,6 @@ impl ConstAllocator {
     /// #![feature(const_trait_impl)]
     /// #![feature(const_mut_refs)]
     /// #![feature(const_option)]
-    /// #![feature(let_else)]
     /// #![const_eval_limit = "500000"]
     /// use core::{alloc::Layout, ptr::NonNull};
     /// use r3_core::utils::{ConstAllocator, Allocator};
@@ -100,7 +99,6 @@ impl ConstAllocator {
     ///
     /// ```rust,compile_fail,E0080
     /// # #![feature(const_trait_impl)]
-    /// # #![feature(let_else)]
     /// # use core::alloc::Layout;
     /// # use r3_core::utils::{ConstAllocator, Allocator};
     /// # const _: () = ConstAllocator::with(doit);

src/r3_kernel/src/lib.rs

@@ -28,7 +28,6 @@
 #![feature(never_type)] // `!`
 #![feature(decl_macro)]
 #![feature(pin_macro)]
-#![feature(let_else)]
 #![feature(doc_cfg)] // `#[doc(cfg(...))]`
 #![deny(unsafe_op_in_unsafe_fn)]
 #![cfg_attr(

src/r3_test_runner/src/main.rs

@@ -4,7 +4,6 @@
 #![feature(lint_reasons)]
 #![feature(decl_macro)] // `macro`
 #![feature(pin_macro)] // `core::pin::pin!`
-#![feature(let_else)] // `let ... = ... else { ... }`
 #![warn(must_not_suspend)]
 use anyhow::Context;
 use clap::Parser;