Migrate test plugins to Rust and async-ify syscall modules

- Replace Python test plugins (echo, ai_test, claudecode) with Rust
  implementations driven by the plugin SDK
- Convert fs/network/process/timer syscall modules to async/await
- Change Network.OpenConn to return stream ConnEvent (conn_id handed
  to client in first "open" frame for Send/Close routing)
- Bind timer callbacks to plugin identity; stream_call subscriptions
  are identity-checked
- Update docs and regenerate Python SDK protobuf stubs

Verified: cargo build/test/clippy clean; echo + ai_test full syscall
suites pass; hermes & claudecode register and heartbeat; cross-plugin
bridge.call routing and auth denial verified end-to-end.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/01-内核系统调用.md

@@ -78,15 +78,18 @@ memory.search(query) -> results
 **管**:对外连接、监听 | **不管**:本地 IPC(内核 gRPC 总线)
 
 ```
-net.request(url, method, body?) -> response
-net.connect(addr, protocol) -> conn
-net.listen(port, protocol) -> listener
-net.send(conn, data)
-net.recv(conn) -> data
-net.close(conn)
-net.available() -> bool
+network.request(url, method, headers?, body?) -> response  # HTTP 请求
+network.open_conn(addr, protocol) -> stream ConnEvent      # TCP 建连,流式推送入站数据
+network.send(conn_id, data)                                # 向已有连接发数据
+network.close(conn_id)                                     # 关闭连接
+network.listen(port, protocol) -> stream ConnEvent         # 监听端口,每 accept 推送 ConnEvent
+network.available() -> bool                                # 网络连通性探测
 ```
 
+gRPC 流式语义:OpenConn/Listen 返回 `stream ConnEvent{conn_id, data, kind}`。
+- 首帧 kind="open"/"accept" 携带 conn_id,后续 kind="data" 携带入站字节,kind="closed" 表示对端关闭。
+- 发送用单独的 `Send` RPC(需传 conn_id),关闭用 `Close` RPC。
+
 ---
 
 ## 6. Process
@@ -115,7 +118,7 @@ proc.list() -> [pid]
 
 ```
 timer.once(delay, callback) -> id  # 到期后通过 PluginBridge.StreamCall 投递事件
-timer.cron(expr, callback) -> id
+timer.cron(expr, callback) -> id   # cron 表达式格式(7段): sec min hour day month weekday year
 timer.cancel(id)
 timer.now() -> timestamp
 ```