Speed up rarity check in index

[casey]

No description provided.

[veryordinally]

I performed some analysis of the distribution of ordinal epochs that we encounter in the rarity checking during indexing various segments of the mainnet:

I also performed a head-to-head comparison of binary search and linear search (by running both versions of the method and got these results from the profiler, indexing from blocks 700000 to 701000:

So binary search takes a total time of about 59s, and linear search takes about 7s, indicating a speedup of a factor of more than 8 on this method.

I will investigate now to what amount of savings that translates overall in an index run.