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/indexmap/benches/faststring.rs

@@ -0,0 +1,183 @@
+#![feature(test)]
+
+extern crate test;
+
+use test::Bencher;
+
+use indexmap::IndexMap;
+
+use std::collections::HashMap;
+
+use std::hash::{Hash, Hasher};
+
+use std::borrow::Borrow;
+use std::ops::Deref;
+
+/// Use a consistently seeded Rng for benchmark stability
+fn small_rng() -> fastrand::Rng {
+    let seed = u64::from_le_bytes(*b"indexmap");
+    fastrand::Rng::with_seed(seed)
+}
+
+#[derive(PartialEq, Eq, Copy, Clone)]
+#[repr(transparent)]
+pub struct OneShot<T: ?Sized>(pub T);
+
+impl Hash for OneShot<str> {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        h.write(self.0.as_bytes())
+    }
+}
+
+impl<'a, S> From<&'a S> for &'a OneShot<str>
+where
+    S: AsRef<str>,
+{
+    #[allow(unsafe_code)]
+    fn from(s: &'a S) -> Self {
+        let s: &str = s.as_ref();
+        // SAFETY: OneShot is a `repr(transparent)` wrapper
+        unsafe { &*(s as *const str as *const OneShot<str>) }
+    }
+}
+
+impl Hash for OneShot<String> {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        h.write(self.0.as_bytes())
+    }
+}
+
+impl Borrow<OneShot<str>> for OneShot<String> {
+    fn borrow(&self) -> &OneShot<str> {
+        <&OneShot<str>>::from(&self.0)
+    }
+}
+
+impl<T> Deref for OneShot<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
+fn shuffled_keys<I>(iter: I) -> Vec<I::Item>
+where
+    I: IntoIterator,
+{
+    let mut v = Vec::from_iter(iter);
+    let mut rng = small_rng();
+    rng.shuffle(&mut v);
+    v
+}
+
+#[bench]
+fn insert_hashmap_string_10_000(b: &mut Bencher) {
+    let c = 10_000;
+    b.iter(|| {
+        let mut map = HashMap::with_capacity(c);
+        for x in 0..c {
+            map.insert(x.to_string(), ());
+        }
+        map
+    });
+}
+
+#[bench]
+fn insert_hashmap_string_oneshot_10_000(b: &mut Bencher) {
+    let c = 10_000;
+    b.iter(|| {
+        let mut map = HashMap::with_capacity(c);
+        for x in 0..c {
+            map.insert(OneShot(x.to_string()), ());
+        }
+        map
+    });
+}
+
+#[bench]
+fn insert_indexmap_string_10_000(b: &mut Bencher) {
+    let c = 10_000;
+    b.iter(|| {
+        let mut map = IndexMap::with_capacity(c);
+        for x in 0..c {
+            map.insert(x.to_string(), ());
+        }
+        map
+    });
+}
+
+#[bench]
+fn lookup_hashmap_10_000_exist_string(b: &mut Bencher) {
+    let c = 10_000;
+    let mut map = HashMap::with_capacity(c);
+    let keys = shuffled_keys(0..c);
+    for &key in &keys {
+        map.insert(key.to_string(), 1);
+    }
+    let lookups = (5000..c).map(|x| x.to_string()).collect::<Vec<_>>();
+    b.iter(|| {
+        let mut found = 0;
+        for key in &lookups {
+            found += map.get(key).is_some() as i32;
+        }
+        found
+    });
+}
+
+#[bench]
+fn lookup_hashmap_10_000_exist_string_oneshot(b: &mut Bencher) {
+    let c = 10_000;
+    let mut map = HashMap::with_capacity(c);
+    let keys = shuffled_keys(0..c);
+    for &key in &keys {
+        map.insert(OneShot(key.to_string()), 1);
+    }
+    let lookups = (5000..c)
+        .map(|x| OneShot(x.to_string()))
+        .collect::<Vec<_>>();
+    b.iter(|| {
+        let mut found = 0;
+        for key in &lookups {
+            found += map.get(key).is_some() as i32;
+        }
+        found
+    });
+}
+
+#[bench]
+fn lookup_indexmap_10_000_exist_string(b: &mut Bencher) {
+    let c = 10_000;
+    let mut map = IndexMap::with_capacity(c);
+    let keys = shuffled_keys(0..c);
+    for &key in &keys {
+        map.insert(key.to_string(), 1);
+    }
+    let lookups = (5000..c).map(|x| x.to_string()).collect::<Vec<_>>();
+    b.iter(|| {
+        let mut found = 0;
+        for key in &lookups {
+            found += map.get(key).is_some() as i32;
+        }
+        found
+    });
+}
+
+#[bench]
+fn lookup_indexmap_10_000_exist_string_oneshot(b: &mut Bencher) {
+    let c = 10_000;
+    let mut map = IndexMap::with_capacity(c);
+    let keys = shuffled_keys(0..c);
+    for &key in &keys {
+        map.insert(OneShot(key.to_string()), 1);
+    }
+    let lookups = (5000..c)
+        .map(|x| OneShot(x.to_string()))
+        .collect::<Vec<_>>();
+    b.iter(|| {
+        let mut found = 0;
+        for key in &lookups {
+            found += map.get(key).is_some() as i32;
+        }
+        found
+    });
+}