Update toolchain, and update macro metavar syntax

The syntax change is needed for perspective to compile on newer
toolchains

the relevant rust repo change is here:
rust-lang/rust@0278505

Signed-off-by: Tom Jakubowski <tom@prospective.dev>

rust/perspective-viewer/rust-toolchain.toml

@@ -11,6 +11,6 @@
 #  ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
 [toolchain]
-channel = "nightly-2023-10-12"
+channel = "nightly-2024-05-07"
 components = ["rustfmt", "clippy", "rust-src"]
 targets = ["wasm32-unknown-unknown"]

rust/perspective-viewer/src/rust/lib.rs

@@ -12,13 +12,11 @@
 
 // Required by yew's `html` macro.
 #![recursion_limit = "1024"]
-#![feature(async_fn_in_trait)]
 #![feature(const_type_name)]
 #![feature(lazy_cell)]
 #![feature(let_chains)]
 #![feature(macro_metavar_expr)]
 #![feature(iter_intersperse)]
-#![feature(return_position_impl_trait_in_trait)]
 #![feature(stmt_expr_attributes)]
 #![warn(
     clippy::all,

rust/perspective-viewer/src/rust/utils/tee.rs

@@ -54,10 +54,10 @@ impl<T: Clone> Tee for T {
 
 macro_rules! gen_tee {
     ($($x:ty),*) => {
-        impl<T: Clone> TeeInternal<{${count(x)} + 1}> for T {
+        impl<T: Clone> TeeInternal<{${count($x)} + 1}> for T {
             type Output = ($($x),*, T);
             fn tee_internal(self) -> Self::Output {
-                ($( ${ignore(x)} self.clone() ),*, self)
+                ($( ${ignore($x)} self.clone() ),*, self)
             }
         }
     };