feat(events): add span events and real-time streaming infrastructure (#21)

* feat(events): add span events and real-time streaming infrastructure

Add new events.py module with:
- EventType constants following OpenTelemetry GenAI conventions
- StreamEvent dataclass for real-time event streaming
- add_event() dual emission (span.add_event + streaming queue)
- Convenience functions for agent, model, tool, and flow events
- EventStream context manager for astream() consumers
- Comprehensive test suite (34 tests)

This enables real-time event streaming while persisting events
to OTel backends (Jaeger, Zipkin, etc.) via span.add_event().

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix(lint): format test_events.py with ruff

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: vilsonrodrigues

src/msgtrace/sdk/__init__.py

@@ -5,11 +5,50 @@
 """
 
 from msgtrace.sdk.attributes import MsgTraceAttributes
+from msgtrace.sdk.events import (
+    EventStream,
+    EventType,
+    StreamEvent,
+    add_agent_complete_event,
+    add_agent_start_event,
+    add_agent_step_event,
+    add_event,
+    add_flow_complete_event,
+    add_flow_reasoning_event,
+    add_flow_step_event,
+    add_model_reasoning_event,
+    add_model_request_event,
+    add_model_response_chunk_event,
+    add_model_response_event,
+    add_tool_call_event,
+    add_tool_error_event,
+    add_tool_result_event,
+)
 from msgtrace.sdk.spans import Spans
 from msgtrace.sdk.tracer import tracer
 
 __all__ = [
+    # Core
     "tracer",
     "Spans",
     "MsgTraceAttributes",
+    # Events
+    "EventType",
+    "StreamEvent",
+    "EventStream",
+    "add_event",
+    # Convenience event functions
+    "add_agent_start_event",
+    "add_agent_complete_event",
+    "add_agent_step_event",
+    "add_model_request_event",
+    "add_model_response_event",
+    "add_model_response_chunk_event",
+    "add_model_reasoning_event",
+    "add_tool_call_event",
+    "add_tool_result_event",
+    "add_tool_error_event",
+    "add_flow_step_event",
+    "add_flow_reasoning_event",
+    "add_flow_complete_event",
 ]