Add aquatic_load_tester: multi-run multi-implementation load tests

- Work in progress
- Only UDP is currently implemented so far
- Also includes some changes to other crates, notably deriving
  serde Serialize for Config structs and making udp_load_test
  a lib and a binary

crates/load_tester/src/main.rs

@@ -0,0 +1,28 @@
+pub mod common;
+pub mod protocols;
+pub mod run;
+pub mod set;
+
+use clap::{Parser, Subcommand};
+
+#[derive(Parser)]
+#[command(author, version, about)]
+struct Args {
+    #[command(subcommand)]
+    command: Command,
+}
+
+#[derive(Subcommand)]
+enum Command {
+    #[cfg(feature = "udp")]
+    Udp(protocols::udp::UdpCommand),
+}
+
+fn main() {
+    let args = Args::parse();
+
+    match args.command {
+        #[cfg(feature = "udp")]
+        Command::Udp(command) => command.run().unwrap(),
+    }
+}