refactor(tracing): replace custom Dapper schemas with OpenTelemetry SDK

[gowthamrao]

Summary

Replaces CoReason's custom Dapper-style distributed tracing schemas (ExecutionSpanReceipt, SpanEvent, TraceExportManifest) with the industry-standard OpenTelemetry SDK and OTLP exporters.

Closes #184

Why?

• Borrow, Don't Build: OpenTelemetry is the absolute industry standard for distributed tracing. Custom span serialization is engineering waste.
• Zero-code LLM tracing: The instructor library (already a dependency) has native OTel auto-instrumentation.
• Zero-code workflow tracing: temporalio (already a dependency) has native OTel interceptors.
• Eliminates ~150 lines of manual JSON validation in EmitSpanIOActivity.

Changes

New Files

• src/coreason_runtime/utils/tracing.py — TracerProvider initialization with OTLP exporter, get_tracer() utility, no-op fallbacks
• tests/utils/test_tracing.py — Comprehensive test suite for the tracing module

Modified Files

File	Change
pyproject.toml	Add opentelemetry-api, opentelemetry-sdk, opentelemetry-exporter-otlp
activities.py	EmitSpanIOActivity now emits real OTel spans instead of validating ExecutionSpanReceipt
logger.py	otel_telemetry_sink replaced — real OTel span emission instead of debug stub
predict_router.py	Initialize TracerProvider to enable instructor auto-instrumentation
test_activities_standalone.py	Updated test_emit_span_valid for OTel-native payloads
test_logger.py	Updated test_otel_telemetry_sink_forwards_message for OTel behavior

NOT in Scope

• ExecutionNodeReceipt stays — it's Merkle-DAG provenance, not tracing
• Schema deprecation in coreason-manifest will be a separate PR (Phase 3 of the plan)

Configuration

Standard OTel env vars:

OTEL_SERVICE_NAME=coreason-runtime
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4317
OTEL_EXPORTER_OTLP_PROTOCOL=grpc

Testing

• ruff format ✅
• ruff check ✅
• mypy ✅ (no new errors; pre-existing DempsterShaferBeliefVector error unchanged)
• pytest — 207 passed, 1 pre-existing failure (test_synthesize_scratch_zero_day_forge)