Important

Modify LangfuseSpanProcessor to use OpenTelemetry's default flush settings when environment variables are not set.

• Behavior:
  • Modify LangfuseSpanProcessor in span_processor.py to use OpenTelemetry's default flush settings when LANGFUSE_FLUSH_AT and LANGFUSE_FLUSH_INTERVAL are not set.
  • flush_at and flush_interval are set to None if environment variables are not provided, allowing OpenTelemetry defaults to apply.

^{This description was created by for eace769. You can customize this summary. It will automatically update as commits are pushed.}