Importer

[Scooletz]

Introduces and Importer that does the import from RocksDb of Nethermind into Paprika's custom storage. To make it work it introduces the following changes:

1. Moves the concept of the Ethereum aware Key away from the PagedDb
2. Makes the SlottedArray is now based or raw ReadOnlySpan<byte> key
3. Introduces StoreKey that allows to efficiently encode Key into a Span<byte> wrapping structure
4. Introduces a mapping of account address to an int as a separate tree in the PagedDb.
   1. This does not decrease the size of the database per se, but as the entries will repeatedly appear for same accounts, should decrease the size of the entry and number of updated pages.
   2. It introduces one additional layer of indirection meaning that the reads and writes will need to read/write through the id tree. It can be amortized later with some caching (this is not done now as it doesn't seem to be needed).
5. Merkle's Node.Branch that is full will have its value encoded as one byte instead of 3. This is a small improvement but should provide some space in upper layers of the PagedDb tree.
6. IBatchContext & co. allows now pages to be RegisterForFutureReuse. Whenever a page is no longer needed it can be abandoned with this call without leaking it out.
7. DataPage has the biggest change introduced with Leaf pages. Whenever the internal map of the page is full but it has no nibble children, it won't have the biggest nibble flushed first. It will use the buckets for addresses to create more pages with maps until they are full. Only once they are full they will be flushed down. This single change reduced the Sepolia size by 40%-50%. Should be observed with Mainnet.

Closes #156

[github-actions]

Package	Line Rate	Branch Rate	Health
Paprika	85%	76%	✔
Summary	85% (2491 / 2917)	76% (671 / 880)	✔

Minimum allowed line rate is 75%