feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/futures-util/benches/bilock.rs

@@ -0,0 +1,68 @@
+#![feature(test)]
+#![cfg(feature = "bilock")]
+
+extern crate test;
+
+use futures::task::Poll;
+use futures_test::task::noop_context;
+use futures_util::lock::BiLock;
+
+use crate::test::Bencher;
+
+#[bench]
+fn contended(b: &mut Bencher) {
+    let mut context = noop_context();
+
+    b.iter(|| {
+        let (x, y) = BiLock::new(1);
+
+        for _ in 0..1000 {
+            let x_guard = match x.poll_lock(&mut context) {
+                Poll::Ready(guard) => guard,
+                _ => panic!(),
+            };
+
+            // Try poll second lock while first lock still holds the lock
+            match y.poll_lock(&mut context) {
+                Poll::Pending => (),
+                _ => panic!(),
+            };
+
+            drop(x_guard);
+
+            let y_guard = match y.poll_lock(&mut context) {
+                Poll::Ready(guard) => guard,
+                _ => panic!(),
+            };
+
+            drop(y_guard);
+        }
+        (x, y)
+    });
+}
+
+#[bench]
+fn lock_unlock(b: &mut Bencher) {
+    let mut context = noop_context();
+
+    b.iter(|| {
+        let (x, y) = BiLock::new(1);
+
+        for _ in 0..1000 {
+            let x_guard = match x.poll_lock(&mut context) {
+                Poll::Ready(guard) => guard,
+                _ => panic!(),
+            };
+
+            drop(x_guard);
+
+            let y_guard = match y.poll_lock(&mut context) {
+                Poll::Ready(guard) => guard,
+                _ => panic!(),
+            };
+
+            drop(y_guard);
+        }
+        (x, y)
+    })
+}