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/syn/benches/file.rs

@@ -0,0 +1,59 @@
+// $ cargo bench --features full,test --bench file
+
+#![feature(rustc_private, test)]
+#![recursion_limit = "1024"]
+#![allow(
+    clippy::elidable_lifetime_names,
+    clippy::items_after_statements,
+    clippy::manual_let_else,
+    clippy::match_like_matches_macro,
+    clippy::missing_panics_doc,
+    clippy::must_use_candidate,
+    clippy::needless_lifetimes,
+    clippy::uninlined_format_args
+)]
+
+extern crate test;
+
+#[macro_use]
+#[path = "../tests/macros/mod.rs"]
+mod macros;
+
+#[allow(dead_code)]
+#[path = "../tests/repo/mod.rs"]
+mod repo;
+
+use proc_macro2::{Span, TokenStream};
+use std::fs;
+use std::str::FromStr;
+use syn::parse::{ParseStream, Parser};
+use test::Bencher;
+
+const FILE: &str = "tests/rust/library/core/src/str/mod.rs";
+
+fn get_tokens() -> TokenStream {
+    repo::clone_rust();
+    let content = fs::read_to_string(FILE).unwrap();
+    TokenStream::from_str(&content).unwrap()
+}
+
+#[bench]
+fn baseline(b: &mut Bencher) {
+    let tokens = get_tokens();
+    b.iter(|| drop(tokens.clone()));
+}
+
+#[bench]
+fn create_token_buffer(b: &mut Bencher) {
+    let tokens = get_tokens();
+    fn immediate_fail(_input: ParseStream) -> syn::Result<()> {
+        Err(syn::Error::new(Span::call_site(), ""))
+    }
+    b.iter(|| immediate_fail.parse2(tokens.clone()));
+}
+
+#[bench]
+fn parse_file(b: &mut Bencher) {
+    let tokens = get_tokens();
+    b.iter(|| syn::parse2::<syn::File>(tokens.clone()));
+}