rust: task: use as_char_ptr instead of as_ptr().cast()

`as_char_ptr` would provide the correct (unsigned char) type without
needing to convert to an intermediate type and cast the pointer.

The `as_ptr()` function is going to be disallowed by clippy warning, so fix
this usage.

This is used only if CONFIG_DEBUG_ATOMIC_SLEEP=y. Instead of conditionally
importing `CStrExt`, import it via prelude instead, and remove other
imports that are already available via the prelude.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601221157.89t3Sqbl-lkp@intel.com/
Signed-off-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260203130745.868762-1-gary@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: nbdd0121

rust/kernel/task.rs

@@ -6,16 +6,15 @@
 
 use crate::{
     bindings,
-    ffi::{c_int, c_long, c_uint},
     mm::MmWithUser,
     pid_namespace::PidNamespace,
+    prelude::*,
     sync::aref::ARef,
     types::{NotThreadSafe, Opaque},
 };
 use core::{
-    cmp::{Eq, PartialEq},
     ops::Deref,
-    ptr,
+    ptr, //
 };
 
 /// A sentinel value used for infinite timeouts.
@@ -419,7 +418,7 @@ pub fn might_sleep() {
         let file = kernel::file_from_location(loc);
 
         // SAFETY: `file.as_ptr()` is valid for reading and guaranteed to be nul-terminated.
-        unsafe { crate::bindings::__might_sleep(file.as_ptr().cast(), loc.line() as i32) }
+        unsafe { crate::bindings::__might_sleep(file.as_char_ptr(), loc.line() as i32) }
     }
 
     // SAFETY: Always safe to call.