Add commitment lookup benchmarking

[antonis19]

Adds a integration commitment bench-lookup --chain=mainnet --datadir <datadir> --sample-size <sample-size> command that bechmarks random key lookups to latest commitment.

Reservoir sampling (https://en.wikipedia.org/wiki/Reservoir_sampling) is used to take a random sample of sample-size keys in one pass.

Some results with a sample of 10M keys from mainnet:

================================================================================
  BENCHMARK RESULTS: Commitment Domain Lookups
================================================================================

  Total Keys in Files: 989960478
  Sampled Keys:        10000000
  Sample Rate:         1.0101%

  Total Lookups:       10000000
  Total Time:          22m34.086304438s
  Throughput:          7380.79 ops/sec
  Avg Value Size:      304.09 bytes

  Latency Statistics:
  -------------------
  Min:                 561ns
  Max:                 94.728663ms
  Mean:                135.408µs
  Std Dev:             146.029µs

  Percentiles:
  ------------
  P50 (Median):        142.716µs
  P90:                 284.412µs
  P95:                 322.403µs
  P99:                 515.173µs
  P99.9:               987.347µs

================================================================================

Geth in comparison:

================================================================================
  BENCHMARK RESULTS: Combined Trie Nodes
================================================================================

  Total Keys in DB:   2452921809
  Sampled Keys:       10000000 (0.4077%)
  Total Lookups:      10000000
  Total Time:         23m59.066456304s
  Throughput:         6945.69 ops/sec
  Avg Value Size:     78.81 bytes

  Latency Statistics:
  -------------------
  Min:                6.422µs
  Max:                25.20701ms
  Mean:               143.906µs
  Std Dev:            61.25µs

  Percentiles:
  ------------
  P50 (Median):       148.208µs
  P90:                183.725µs
  P95:                202.9µs
  P99:                254.067µs
  P99.9:              336.441µs

================================================================================