containers: Docker (and best-effort Podman) plugin

- minimal Docker Engine API client over Unix/TCP sockets with version
  negotiation and chunked response decoding
- drop-in stats schema: active/stopped containers, CPU/memory/IO/network
  rates, ports, uptime (pretty_date), image, engine field
- Docker + Podman engines, config (all, podman_sock, max_name_size,
  disable_stats, show/hide, per-container thresholds)
- export strips the computation sub-dicts (--stdout/--stdout-csv)
- TUI block above the process count
- CI-safe fake Docker socket test + live differential parity

crates/glances-plugins/src/engine.rs

@@ -31,6 +31,10 @@ impl Engine {
             "amps".to_string(),
             Box::new(AmpsPlugin::new(&config, &args)),
         );
+        plugins.insert(
+            "containers".to_string(),
+            Box::new(ContainersPlugin::new(&config, &args)),
+        );
         plugins.insert(
             "core".to_string(),
             Box::new(CorePlugin::new(&config, &args)),