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>

plugins/hermes/hermes_plugin.py

@@ -45,8 +45,10 @@ logger = logging.getLogger(__name__)
 class HermesPlugin:
     """Bridges Hermes tools into agentsd."""
 
-    def __init__(self, agentsd_addr: str = "localhost:50051"):
-        self.addr = agentsd_addr
+    def __init__(self, agentsd_addr: str = None):
+        # agentsd binds [::1]:50051 (IPv6 loopback); match it so "localhost"
+        # resolving to IPv4 first doesn't break the connection. AGENTSD_ADDR overrides.
+        self.addr = agentsd_addr or os.environ.get("AGENTSD_ADDR", "[::1]:50051")
         self.channel = None
         self.bridge = None
         self.registry = None