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/futures_unordered.rs

@@ -0,0 +1,43 @@
+#![feature(test)]
+
+extern crate test;
+use crate::test::Bencher;
+
+use futures::channel::oneshot;
+use futures::executor::block_on;
+use futures::future;
+use futures::stream::{FuturesUnordered, StreamExt};
+use futures::task::Poll;
+use std::collections::VecDeque;
+use std::thread;
+
+#[bench]
+fn oneshots(b: &mut Bencher) {
+    const NUM: usize = 10_000;
+
+    b.iter(|| {
+        let mut txs = VecDeque::with_capacity(NUM);
+        let mut rxs = FuturesUnordered::new();
+
+        for _ in 0..NUM {
+            let (tx, rx) = oneshot::channel();
+            txs.push_back(tx);
+            rxs.push(rx);
+        }
+
+        thread::spawn(move || {
+            while let Some(tx) = txs.pop_front() {
+                let _ = tx.send("hello");
+            }
+        });
+
+        block_on(future::poll_fn(move |cx| {
+            loop {
+                if let Poll::Ready(None) = rxs.poll_next_unpin(cx) {
+                    break;
+                }
+            }
+            Poll::Ready(())
+        }))
+    });
+}