rust: time: Seal the HrTimerMode trait

Prevent downstream crates or drivers from implementing `HrTimerMode`
for arbitrary types, which could otherwise leads to unsupported
behavior.

Introduce a `private::Sealed` trait and implement it for all types
that implement `HrTimerMode`.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250617232806.3950141-1-fujita.tomonori@gmail.com
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

Author: fujita

rust/kernel/time/hrtimer.rs

@@ -444,8 +444,27 @@ impl HrTimerExpires for Delta {
     }
 }
 
+mod private {
+    use crate::time::ClockSource;
+
+    pub trait Sealed {}
+
+    impl<C: ClockSource> Sealed for super::AbsoluteMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativeMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsolutePinnedMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativePinnedMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsoluteSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativeSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsolutePinnedSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativePinnedSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsoluteHardMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativeHardMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsolutePinnedHardMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativePinnedHardMode<C> {}
+}
+
 /// Operational mode of [`HrTimer`].
-pub trait HrTimerMode {
+pub trait HrTimerMode: private::Sealed {
     /// The C representation of hrtimer mode.
     const C_MODE: bindings::hrtimer_mode;