[feature] Uniform index format

[andll]

• Benchmark
  • Confirm ~2x less latency with single thread benchmark
  • Compare maximum throughput against micro-cell index format with multi-thread benchmark
  • Function of index size (10k .. 1M)
• Window size table
• Compare stress test results
• Allow to select/configure index format per key-space
• Support on-disk iterators for both index formats
• Incorporate binary search approach into HeaderLookup index