docs: add Realistic and Heavily quoted rows to benchmark table

[nnnkkk7]

Summary

• Add Realistic (40% quoted) row: 4/10 fields quoted with embedded commas, 6 plain — exercises PCLMULQDQ prefix-XOR on partial data
• Add Heavily quoted fields row: all-quoted worst case at 100K rows
• Update Note to describe what each workload tests

Test plan

• Fill in ? values after running BenchmarkReadAll_Realistic_100K and BenchmarkReadAll_Quoted_100K on the AVX-512 self-hosted runner