Add cube-bench (correctness-gated microbenchmarks) + daemon stats telemetry

- cube-bench crate: real-code-path throughput/latency over cubestore,
  cubecrypt (aes/gcm/chacha/xts), cubecode VM, and cubesys Session.
  Every section asserts correctness before timing. Wired into ./check
  as an opt-in 'bench' stage.
- cubesys Session: per-command latency histogram + per-C-namespace record
  counts, exposed via a new 'stats' command over the live socket.
- Deployed rebuilt cube-server to /home/luulu/.cubelinux/bin and
  restarted the system cube.service; verified stats live.

cube-bench/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "cube-bench"
+version = "0.1.0"
+edition = "2021"
+# Correctness-gated microbenchmarks for CUBELinux-2.
+# Runs as a plain `cargo run -p cube-bench`; every measurement path first
+# asserts an invariant so a silent regression cannot masquerade as a result.
+
+[dependencies]
+cubecoords = { path = "../cubecoords" }
+cubestore  = { path = "../cubestore" }
+cubecrypt  = { path = "../cubecrypt" }
+cubecode   = { path = "../cubecode" }
+cubesys    = { path = "../cubesys" }
+
+[dev-dependencies]