Recsplit experiments (#2706)

* Only do 2m

* Optimisation

* Flexible count

* Count properly

* count

* Bijection check

* Add keys

* Print bucket info

* Collision map

* Collision map

* Add tracing

* Tracing

* Fix split

* No trace, print lookup time

* Not override count if block=0

* fix count

* Go mod tidy

* Fix lint

* Measurements

* Cleanup

* Latest erigon-lib

Co-authored-by: Alexey Sharp <alexeysharp@Alexeys-iMac.local>
Co-authored-by: Alex Sharp <alexsharp@Alexs-MacBook-Pro.local>