New page buffer management

[Scooletz]

This PR changes the way data are stored in-page from frame based to a modified slot array. A slot array uses a slice of memory to store two growing sets of data, one from the beginning, one from the end. The one growing from the beginning is responsible for storing metadata entries called Slots. The one growing from the end, the data.

In case of Paprika a modified version is used, called FixedMap, that with some overhead, is self-sufficient in handling keys and no external indexing is required.

The FixedMap is size agnostic so can be used in any type of pages out there.

Paprika.Runner

The run of Paprika.Runner shows the reduction by ~20% of the disk space and according reduction of the pages allocated. This is a good indicator to move forward with #22.

Before (main)

Writing state of 1000 accounts per block through 2000 blocks, generated 2000000 accounts, used 5.67GB
Reading state of all of 2000000 accounts from the last block took 00:00:00.2241420
90th percentiles:
   - new pages allocated per block: 943
   - pages reused allocated per block: 1020
   - total pages written per block: 1963

After (this branch)

Writing state of 1000 accounts per block through 2000 blocks, generated 2000000 accounts, used 4.76GB
Reading state of all of 2000000 accounts from the last block took 00:00:00.3171895
90th percentiles:
   - new pages allocated per block: 868
   - pages reused allocated per block: 1019
   - total pages written per block: 1887

Resolves #23

[github-actions]

Package	Line Rate	Branch Rate	Health
Paprika	89%	77%	✔
Summary	89% (1017 / 1140)	77% (245 / 318)	✔

Minimum allowed line rate is 75%