Refactor stats to use atomics (#375)

* Refactor stats to use atomics

When we are dealing with a high number of connections, generated
stats cannot be consumed fast enough by the stats collector loop.
This makes the stats subsystem inconsistent and a log of
warning messages are thrown due to unregistered server/clients.

This change refactors the stats subsystem so it uses atomics:

- Now counters are handled using U64 atomics
- Event system is dropped and averages are calculated using a loop
  every 15 seconds.
- Now, instead of snapshots being generated ever second we keep track of servers/clients
  that have registered. Each pool/server/client has its own instance of the counter and
  makes changes directly, instead of adding an event that gets processed later.

* Manually mplement Hash/Eq in `config::Address` ignoring stats

* Add tests for client connection counters

* Allow connecting to dockerized dev pgcat from the host

* stats: Decrease cl_idle when idle socket disconnects

src/main.rs

@@ -162,8 +162,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         let client_server_map: ClientServerMap = Arc::new(Mutex::new(HashMap::new()));
 
         // Statistics reporting.
-        let (stats_tx, stats_rx) = mpsc::channel(500_000);
-        REPORTER.store(Arc::new(Reporter::new(stats_tx.clone())));
+        REPORTER.store(Arc::new(Reporter::default()));
 
         // Connection pool that allows to query all shards and replicas.
         match ConnectionPool::from_config(client_server_map.clone()).await {
@@ -175,7 +174,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         };
 
         tokio::task::spawn(async move {
-            let mut stats_collector = Collector::new(stats_rx, stats_tx.clone());
+            let mut stats_collector = Collector::default();
             stats_collector.collect().await;
         });