bevy_tasks: Apply #[deny(clippy::allow_attributes, clippy::allow_attributes_without_reason)] (#17089)

# Objective
We want to deny the following lints:
* `clippy::allow_attributes` - Because there's no reason to
`#[allow(...)]` an attribute if it wouldn't lint against anything; you
should always use `#[expect(...)]`
* `clippy::allow_attributes_without_reason` - Because documenting the
reason for allowing/expecting a lint is always good

## Solution
Set the `clippy::allow_attributes` and
`clippy::allow_attributes_without_reason` lints to `deny`, and bring
`bevy_tasks` in line with the new restrictions.

No code changes have been made - except if a lint that was previously
`allow(...)`'d could be removed via small code changes. For example,
`unused_variables` can be handled by adding a `_` to the beginning of a
field's name.

## Testing
I ran `cargo clippy`, and received no errors.

crates/bevy_tasks/src/executor.rs

@@ -50,6 +50,7 @@ pub struct LocalExecutor<'a>(LocalExecutorInner<'a>);
 
 impl Executor<'_> {
     /// Construct a new [`Executor`]
+    #[expect(clippy::allow_attributes, reason = "This lint may not always trigger.")]
     #[allow(dead_code, reason = "not all feature flags require this function")]
     pub const fn new() -> Self {
         Self(ExecutorInner::new())
@@ -58,6 +59,7 @@ impl Executor<'_> {
 
 impl LocalExecutor<'_> {
     /// Construct a new [`LocalExecutor`]
+    #[expect(clippy::allow_attributes, reason = "This lint may not always trigger.")]
     #[allow(dead_code, reason = "not all feature flags require this function")]
     pub const fn new() -> Self {
         Self(LocalExecutorInner::new())

crates/bevy_tasks/src/lib.rs

@@ -5,6 +5,7 @@
     html_favicon_url = "https://bevyengine.org/assets/icon.png"
 )]
 #![cfg_attr(not(feature = "std"), no_std)]
+#![deny(clippy::allow_attributes, clippy::allow_attributes_without_reason)]
 
 extern crate alloc;
 

crates/bevy_tasks/src/task_pool.rs

@@ -694,7 +694,6 @@ where
 }
 
 #[cfg(test)]
-#[allow(clippy::disallowed_types)]
 mod tests {
     use super::*;
     use core::sync::atomic::{AtomicBool, AtomicI32, Ordering};