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)

crates/xserial-client/src/lib.rs

@@ -0,0 +1,15 @@
+pub mod config;
+pub mod event;
+pub mod cmd;
+pub mod error;
+pub mod history;
+pub mod session;
+pub mod manager;
+pub mod lua;
+
+pub use config::{DecoderConfig, FramerConfig, PipelineConfig, SessionConfig};
+pub use error::{Error, Result};
+pub use event::DecodedEntry;
+pub use history::RingBuffer;
+pub use manager::SessionManager;
+pub use session::{Session, SessionEvent, SessionHandle, SessionId};