chore: introduce AppEventSender to help fix clippy warnings and update to Rust 1.87 (#948)

Moving to Rust 1.87 introduced a clippy warning that
`SendError<AppEvent>` was too large.

In practice, the only thing we ever did when we got this error was log
it (if the mspc channel is closed, then the app is likely shutting down
or something, so there's not much to do...), so this finally motivated
me to introduce `AppEventSender`, which wraps
`std::sync::mpsc::Sender<AppEvent>` with a `send()` method that invokes
`send()` on the underlying `Sender` and logs an `Err` if it gets one.

This greatly simplifies the code, as many functions that previously
returned `Result<(), SendError<AppEvent>>` now return `()`, so we don't
have to propagate an `Err` all over the place that we don't really
handle, anyway.

This also makes it so we can upgrade to Rust 1.87 in CI.

codex-rs/tui/src/status_indicator_widget.rs

@@ -5,7 +5,6 @@ use std::sync::Arc;
 use std::sync::atomic::AtomicBool;
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering;
-use std::sync::mpsc::Sender;
 use std::thread;
 use std::time::Duration;
 
@@ -26,6 +25,7 @@ use ratatui::widgets::Paragraph;
 use ratatui::widgets::WidgetRef;
 
 use crate::app_event::AppEvent;
+use crate::app_event_sender::AppEventSender;
 
 use codex_ansi_escape::ansi_escape_line;
 
@@ -45,12 +45,12 @@ pub(crate) struct StatusIndicatorWidget {
     // animation thread is still running. The field itself is currently not
     // accessed anywhere, therefore the leading underscore silences the
     // `dead_code` warning without affecting behavior.
-    _app_event_tx: Sender<AppEvent>,
+    _app_event_tx: AppEventSender,
 }
 
 impl StatusIndicatorWidget {
     /// Create a new status indicator and start the animation timer.
-    pub(crate) fn new(app_event_tx: Sender<AppEvent>, height: u16) -> Self {
+    pub(crate) fn new(app_event_tx: AppEventSender, height: u16) -> Self {
         let frame_idx = Arc::new(AtomicUsize::new(0));
         let running = Arc::new(AtomicBool::new(true));
 
@@ -65,9 +65,7 @@ impl StatusIndicatorWidget {
                     std::thread::sleep(Duration::from_millis(200));
                     counter = counter.wrapping_add(1);
                     frame_idx_clone.store(counter, Ordering::Relaxed);
-                    if app_event_tx_clone.send(AppEvent::Redraw).is_err() {
-                        break;
-                    }
+                    app_event_tx_clone.send(AppEvent::Redraw);
                 }
             });
         }