bevy_ptr: fix unsafe_op_in_unsafe_fn lint (bevyengine#11610)

# Objective

- Part of bevyengine#11590

## Solution

Fix `unsafe_op_in_unsafe_fn` for `bevy_ptr`.

crates/bevy_ptr/src/lib.rs

@@ -1,8 +1,6 @@
 #![doc = include_str!("../README.md")]
 #![no_std]
 #![warn(missing_docs)]
-// FIXME(11590): remove this once the lint is fixed
-#![allow(unsafe_op_in_unsafe_fn)]
 
 use core::fmt::{self, Formatter, Pointer};
 use core::{
@@ -106,7 +104,8 @@ macro_rules! impl_ptr {
             #[inline]
             pub unsafe fn byte_offset(self, count: isize) -> Self {
                 Self(
-                    NonNull::new_unchecked(self.as_ptr().offset(count)),
+                    // SAFETY: The caller upholds safety for `offset` and ensures the result is not null.
+                    unsafe { NonNull::new_unchecked(self.as_ptr().offset(count)) },
                     PhantomData,
                 )
             }
@@ -126,7 +125,8 @@ macro_rules! impl_ptr {
             #[inline]
             pub unsafe fn byte_add(self, count: usize) -> Self {
                 Self(
-                    NonNull::new_unchecked(self.as_ptr().add(count)),
+                    // SAFETY: The caller upholds safety for `add` and ensures the result is not null.
+                    unsafe { NonNull::new_unchecked(self.as_ptr().add(count)) },
                     PhantomData,
                 )
             }
@@ -176,7 +176,9 @@ impl<'a, A: IsAligned> Ptr<'a, A> {
     ///   for the pointee type `T`.
     #[inline]
     pub unsafe fn deref<T>(self) -> &'a T {
-        &*self.as_ptr().cast::<T>().debug_ensure_aligned()
+        let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
+        // SAFETY: The caller ensures the pointee is of type `T` and the pointer can be dereferenced.
+        unsafe { &*ptr }
     }
 
     /// Gets the underlying pointer, erasing the associated lifetime.
@@ -230,7 +232,9 @@ impl<'a, A: IsAligned> PtrMut<'a, A> {
     ///   for the pointee type `T`.
     #[inline]
     pub unsafe fn deref_mut<T>(self) -> &'a mut T {
-        &mut *self.as_ptr().cast::<T>().debug_ensure_aligned()
+        let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
+        // SAFETY: The caller ensures the pointee is of type `T` and the pointer can be dereferenced.
+        unsafe { &mut *ptr }
     }
 
     /// Gets the underlying pointer, erasing the associated lifetime.
@@ -299,7 +303,9 @@ impl<'a, A: IsAligned> OwningPtr<'a, A> {
     ///   for the pointee type `T`.
     #[inline]
     pub unsafe fn read<T>(self) -> T {
-        self.as_ptr().cast::<T>().debug_ensure_aligned().read()
+        let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
+        // SAFETY: The caller ensure the pointee is of type `T` and uphold safety for `read`.
+        unsafe { ptr.read() }
     }
 
     /// Consumes the [`OwningPtr`] to drop the underlying data of type `T`.
@@ -310,10 +316,11 @@ impl<'a, A: IsAligned> OwningPtr<'a, A> {
     ///   for the pointee type `T`.
     #[inline]
     pub unsafe fn drop_as<T>(self) {
-        self.as_ptr()
-            .cast::<T>()
-            .debug_ensure_aligned()
-            .drop_in_place();
+        let ptr = self.as_ptr().cast::<T>().debug_ensure_aligned();
+        // SAFETY: The caller ensure the pointee is of type `T` and uphold safety for `drop_in_place`.
+        unsafe {
+            ptr.drop_in_place();
+        }
     }
 
     /// Gets the underlying pointer, erasing the associated lifetime.
@@ -346,7 +353,9 @@ impl<'a> OwningPtr<'a, Unaligned> {
     /// # Safety
     /// - `T` must be the erased pointee type for this [`OwningPtr`].
     pub unsafe fn read_unaligned<T>(self) -> T {
-        self.as_ptr().cast::<T>().read_unaligned()
+        let ptr = self.as_ptr().cast::<T>();
+        // SAFETY: The caller ensure the pointee is of type `T` and uphold safety for `read_unaligned`.
+        unsafe { ptr.read_unaligned() }
     }
 }
 
@@ -368,7 +377,9 @@ impl<'a, T> ThinSlicePtr<'a, T> {
         #[cfg(debug_assertions)]
         debug_assert!(index < self.len);
 
-        &*self.ptr.as_ptr().add(index)
+        let ptr = self.ptr.as_ptr();
+        // SAFETY: `index` is in-bounds so the resulting pointer is valid to dereference.
+        unsafe { &*ptr.add(index) }
     }
 }
 
@@ -435,19 +446,22 @@ pub trait UnsafeCellDeref<'a, T>: private::SealedUnsafeCell {
 impl<'a, T> UnsafeCellDeref<'a, T> for &'a UnsafeCell<T> {
     #[inline]
     unsafe fn deref_mut(self) -> &'a mut T {
-        &mut *self.get()
+        // SAFETY: The caller upholds the alias rules.
+        unsafe { &mut *self.get() }
     }
     #[inline]
     unsafe fn deref(self) -> &'a T {
-        &*self.get()
+        // SAFETY: The caller upholds the alias rules.
+        unsafe { &*self.get() }
     }
 
     #[inline]
     unsafe fn read(self) -> T
     where
         T: Copy,
     {
-        self.get().read()
+        // SAFETY: The caller upholds the alias rules.
+        unsafe { self.get().read() }
     }
 }