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/common/src/privileges.rs

@@ -5,11 +5,11 @@ use std::{
 
 use anyhow::Context;
 use privdrop::PrivDrop;
-use serde::Deserialize;
+use serde::{Deserialize, Serialize};
 
 use aquatic_toml_config::TomlConfig;
 
-#[derive(Clone, Debug, PartialEq, TomlConfig, Deserialize)]
+#[derive(Clone, Debug, PartialEq, TomlConfig, Deserialize, Serialize)]
 #[serde(default, deny_unknown_fields)]
 pub struct PrivilegeConfig {
     /// Chroot and switch group and user after binding to sockets