refactor: mark enabled ephemeral timer duration as NonZero

Now the type system ensures that Timer::Enabled
never stores 0 value inside accidentally,
it is impossible to put 0 there without unsafe code.

src/chat.rs

@@ -1899,7 +1899,7 @@ impl Chat {
         };
         let ephemeral_timestamp = match ephemeral_timer {
             EphemeralTimer::Disabled => 0,
-            EphemeralTimer::Enabled { duration } => time().saturating_add(duration.into()),
+            EphemeralTimer::Enabled { duration } => time().saturating_add(duration.get().into()),
         };
 
         let (msg_text, was_truncated) = truncate_msg_text(context, msg.text.clone()).await?;