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/zerocopy-derive/tests/union_try_from_bytes.rs

@@ -0,0 +1,140 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+// See comment in `include.rs` for why we disable the prelude.
+#![no_implicit_prelude]
+#![allow(warnings)]
+
+include!("include.rs");
+
+// A struct is `imp::TryFromBytes` if:
+// - any of its fields are `imp::TryFromBytes`
+
+#[derive(imp::Immutable, imp::TryFromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+union One {
+    a: u8,
+}
+
+util_assert_impl_all!(One: imp::TryFromBytes);
+
+#[test]
+fn one() {
+    crate::util::test_is_bit_valid::<One, _>([42u8], true);
+    crate::util::test_is_bit_valid::<One, _>([43u8], true);
+}
+
+#[derive(imp::Immutable, imp::TryFromBytes, imp::IntoBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union Two {
+    a: bool,
+    b: bool,
+}
+
+util_assert_impl_all!(Two: imp::TryFromBytes);
+
+#[test]
+fn two() {
+    crate::util::test_is_bit_valid::<Two, _>(Two { a: false }, true);
+    crate::util::test_is_bit_valid::<Two, _>(Two { b: true }, true);
+    crate::util::test_is_bit_valid::<Two, _>([2u8], false);
+}
+
+#[derive(imp::Immutable, imp::TryFromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union BoolAndZst {
+    a: bool,
+    b: (),
+}
+
+#[test]
+fn bool_and_zst() {
+    crate::util::test_is_bit_valid::<BoolAndZst, _>([0u8], true);
+    crate::util::test_is_bit_valid::<BoolAndZst, _>([1u8], true);
+    crate::util::test_is_bit_valid::<BoolAndZst, _>([2u8], true);
+}
+
+#[derive(imp::FromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union MaybeFromBytes<T: imp::Copy> {
+    t: T,
+}
+
+#[test]
+fn test_maybe_from_bytes() {
+    // When deriving `FromBytes` on a type with no generic parameters, we emit a
+    // trivial `is_bit_valid` impl that always returns true. This test confirms
+    // that we *don't* spuriously do that when generic parameters are present.
+
+    crate::util::test_is_bit_valid::<MaybeFromBytes<bool>, _>([2u8], false);
+}
+
+#[derive(imp::Immutable, imp::TryFromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union TypeParams<'a, T: imp::Copy, I: imp::Iterator>
+where
+    I::Item: imp::Copy,
+{
+    a: I::Item,
+    b: u8,
+    c: imp::PhantomData<&'a [u8]>,
+    d: imp::PhantomData<&'static str>,
+    e: imp::PhantomData<imp::String>,
+    f: T,
+}
+
+util_assert_impl_all!(TypeParams<'static, (), imp::IntoIter<()>>: imp::TryFromBytes);
+util_assert_impl_all!(TypeParams<'static, util::AU16, imp::IntoIter<()>>: imp::TryFromBytes);
+util_assert_impl_all!(TypeParams<'static, [util::AU16; 2], imp::IntoIter<()>>: imp::TryFromBytes);
+
+// Deriving `imp::TryFromBytes` should work if the union has bounded parameters.
+
+#[derive(imp::Immutable, imp::TryFromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + imp::TryFromBytes, const N: usize>
+where
+    'a: 'b,
+    'b: 'a,
+    T: 'a + 'b + imp::TryFromBytes + imp::Copy,
+{
+    a: imp::PhantomData<&'a &'b ()>,
+    b: T,
+}
+
+util_assert_impl_all!(WithParams<'static, 'static, u8, 42>: imp::TryFromBytes);
+
+#[derive(Clone, Copy, imp::TryFromBytes, imp::Immutable)]
+#[zerocopy(crate = "zerocopy_renamed")]
+struct A;
+
+#[derive(imp::TryFromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+union B {
+    a: A,
+}
+
+#[derive(imp::TryFromBytes)]
+#[zerocopy(crate = "zerocopy_renamed")]
+#[repr(C)]
+union UnsafeCellUnion {
+    a: imp::ManuallyDrop<imp::UnsafeCell<bool>>,
+}
+
+util_assert_impl_all!(UnsafeCellUnion: imp::TryFromBytes);
+
+#[test]
+fn unsafe_cell_union() {
+    crate::util::test_is_bit_valid::<UnsafeCellUnion, _>([0u8], true);
+    crate::util::test_is_bit_valid::<UnsafeCellUnion, _>([1u8], true);
+    crate::util::test_is_bit_valid::<UnsafeCellUnion, _>([2u8], false);
+}