add tool to collect histogram of CLVM back-reference lengths

[arvidn]

This is a survey tool to aid in optimizing serialization (with back-references). This tool looks at all back references in block generators, recording how many bytes of path they use. The output is a histogram, counting the frequency of each length (in bytes).

On mainnet, the output looks like this:

  1: 14138519
  2: 3535917
  3: 7757043
  4: 4411544
  5: 1950464
  6: 2847272
  7: 3035066
  8: 1511823
  9: 401799
 10: 335581
 11: 193567
 12: 177828
 13: 30668
 14: 43426
 15: 25351
 16: 20269
 17: 14484
 18: 12950
 19: 12858
 20: 12106
 21: 11844
 22: 10967
 23: 10945
 24: 9841
 25: 9361
 26: 10244
 27: 10315
 28: 10272
 29: 9789
 30: 8842
 31: 8566
 32: 8946
 33: 2470
 34: 2350
 35: 2218
 36: 2120
 37: 1942
 38: 1941
 39: 1915
 40: 1927
 41: 1919
 42: 1910
 43: 1906
 44: 1899
 45: 1898
 46: 1911
 47: 1892
 48: 1899
 49: 176
 50: 176
 51: 174
 52: 189
 53: 190
 54: 136
 55: 98
 56: 100
 57: 84
 58: 86
 59: 84
 60: 79
 61: 83
 62: 84
 63: 81
 64: 78
 65: 97
 66: 82
 67: 95
 68: 81
 69: 84
 70: 80
 71: 78
 72: 73
 73: 74
 74: 73
 75: 74
 76: 65
 77: 61
 78: 69
 79: 65
 80: 64
 81: 62
 82: 61
 83: 61
 84: 63
 85: 62
 86: 63
 87: 6
 88: 5
 89: 1
 90: 1
 91: 1
 93: 1
100: 1
102: 1
103: 7
104: 2
105: 2
109: 2
111: 1
112: 1
114: 1
115: 6
117: 1
119: 2
121: 1
130: 3
132: 1
133: 1
136: 1
138: 1
139: 1
140: 1
141: 2
143: 1
153: 1
157: 1
165: 1

[coveralls-official]

Pull Request Test Coverage Report for Build 12575130458

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 83.972%

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Totals
Change from base Build 12575129443:	0.0%
Covered Lines:	13349
Relevant Lines:	15897

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