docs: replace common enrichment patterns with enrich_span_context section

- Remove Pattern 1-5 (common enrichment patterns) from span enrichment guide
- Add comprehensive section on enrich_span_context() for inline span creation
- Emphasize use case: when it's hard to split code into separate functions
- Include comparison table: @trace decorator vs enrich_span_context()
- Add real-world RAG pipeline example with inline spans
- Provide clear guidance on when to use each approach
- Reduce doc from 757 to 544 lines (more focused on key patterns)

Author: codehruv