test: add the HyperHDR mock server and the integration tests

The mock imitates FlatBuffersServerConnection and FlatBuffersParser (spec
3.2), including the priority handling, the idle timeout and the reject paths,
so the client can be tested against it over a real socket. It doubles as a
standalone example binary for end-to-end runs.

examples/mock_hyperhdr.rs

@@ -0,0 +1,60 @@
+//! Standalone HyperHDR flatbuffers server mock, the same code the integration tests use.
+//!
+//! cargo run --example mock_hyperhdr -- --listen 127.0.0.1:19400
+
+use std::io::IsTerminal;
+use std::time::Duration;
+
+use clap::{Parser, ValueEnum};
+use gamescope_hyperhdr::hyperhdr::mock::{Behavior, MockOptions, MockServer};
+use tracing::info;
+
+#[derive(Debug, Clone, Copy, ValueEnum)]
+enum Mode {
+    Normal,
+    Reject,
+    NoRead,
+    ErrorReplies,
+}
+
+#[derive(Parser)]
+#[command(about = "Imitation of HyperHDR's flatbuffers server")]
+struct Opt {
+    /// Address to listen on
+    #[arg(long, default_value = "127.0.0.1:19400")]
+    listen: String,
+    /// Close connections after this many seconds without data (HyperHDR's `timeout`)
+    #[arg(long, default_value_t = 5)]
+    timeout_secs: u64,
+    /// How to treat connections
+    #[arg(long, value_enum, default_value_t = Mode::Normal)]
+    behavior: Mode,
+}
+
+fn main() -> anyhow::Result<()> {
+    let opt = Opt::parse();
+    tracing_subscriber::fmt()
+        .with_target(false)
+        .with_writer(std::io::stderr)
+        .with_ansi(std::io::stderr().is_terminal())
+        .init();
+
+    let server = MockServer::start(
+        opt.listen.as_str(),
+        MockOptions {
+            idle_timeout: Duration::from_secs(opt.timeout_secs),
+            record_events: false,
+            log_events: true,
+        },
+    )?;
+    server.set_behavior(match opt.behavior {
+        Mode::Normal => Behavior::Normal,
+        Mode::Reject => Behavior::Reject,
+        Mode::NoRead => Behavior::NoRead,
+        Mode::ErrorReplies => Behavior::ErrorReplies,
+    });
+    info!("listening on {} ({:?})", server.addr(), opt.behavior);
+    loop {
+        std::thread::park();
+    }
+}