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/Cargo.toml

@@ -16,3 +16,6 @@ sysinfo = "0.39.6"
 thiserror.workspace = true
 tracing.workspace = true
 ureq = { version = "3.4.2", features = ["json"] }
+
+[dev-dependencies]
+clap = { workspace = true, features = ["derive"] }