feat: xserial-client with session management, mlua integration, and 238 tests

- Session: background I/O task with SessionHandle for send/read/close/reconfigure
- SessionManager: multi-session collection with aggregated event broadcast
- Config: serializable SessionConfig/PipelineConfig/FramerConfig/DecoderConfig
- Lua: xserial global (open/list_ports/sleep/log) + session userdata API
- RingBuffer: bounded history buffer with pipeline filtering
- Core: added Serialize/Deserialize+Default to Endian/TextEncoding/PlotFormat
- Core: added Send bound to Framer trait for tokio task compatibility
- 238 tests (193 core + 10 config + 7 Lua + 9 session + 18 pipeline + 1 doctest)

Cargo.toml

@@ -50,5 +50,5 @@ egui = "0.34"
 eframe = "0.34"
 egui_plot = "0.35"
 
-# ── Lua (Step 6 启用) ──
-# mlua = { version = "0.11", features = ["luajit", "async", "serde", "send", "macros", "vendored"] }
+# ── Lua ──
+mlua = { version = "0.11", features = ["luajit", "async", "serde", "send", "macros", "vendored"] }