feat: Add handler-base library for NATS AI/ML services

- Handler base class with graceful shutdown and signal handling
- NATSClient with JetStream and msgpack serialization
- Pydantic Settings for environment configuration
- HealthServer for Kubernetes probes
- OpenTelemetry telemetry setup
- Service clients: STT, TTS, LLM, Embeddings, Reranker, Milvus

handler_base/__init__.py

@@ -0,0 +1,27 @@
+"""
+Handler Base - Shared utilities for AI/ML handler services.
+
+Provides consistent patterns for:
+- OpenTelemetry tracing and metrics
+- NATS messaging
+- Health checks
+- Graceful shutdown
+- Service client wrappers
+"""
+from handler_base.config import Settings
+from handler_base.handler import Handler
+from handler_base.health import HealthServer
+from handler_base.nats_client import NATSClient
+from handler_base.telemetry import setup_telemetry, get_tracer, get_meter
+
+__all__ = [
+    "Handler",
+    "Settings",
+    "HealthServer",
+    "NATSClient",
+    "setup_telemetry",
+    "get_tracer",
+    "get_meter",
+]
+
+__version__ = "1.0.0"