Lmdb visualisation + freelist stability fixes (#1345)

* Visualisations

* Use graphviz records

* Fix lint

* Fix lint

* Reduced leaf pages

* Fix

* Overflow pages

* Fix lint

* Fix lint

* Fix lint

* Add dupsort generate

* DupSort experiments

* Add dupsort nodes

* More interesting dupsort

* freelist

* Fragmented freelist

* Fix lint

* drop T2 too

* Handle overflow pages in FREE_DBI

* Skipping in the MAIN_DBI leaves

* Switch to double-tap LMDB

* Fix to double-tap

* With/without reader visualisations

* Flip flopping without reader

* Tidy mods

* Fix lint, switch to new lmdb-go release

* mod tidy