[KVStore] Implement RocksDB as a KVStore submodule

[h5law]

Objective

Implement a submodule in the kvstore directory for a RocksDB

• Look into IOTA's rocksdb and see whether this can be used. The repo
• Look into Pebble by CockroachDB a Go implementation based on RocksDB they use at CockroachDB
• Look into grocksdb which is a wrapper in Go for RocksDB being actively maintained
• Look into gorocksdb developed by cosmos as their Go wrapper for RocksDB

Origin Document

RocksDB is known for its speed and effiiency, having it not only as a nodestore backing the SMT would improve performance in prod but also a wrapper around RocksDB that exposes extra methods would be highly sought after.

Goals

• Find an appropriate library to base the submodule on
• Create a submodule and expose an interface for easy use
• Ensure it conforms to MapStore and can be used with the SMT
• Add documentation

Deliverables

• Create a RocksDB submodule with wrapping functions to provide extra capabilities
• Add extensive testing
• Add documentation
• Add runnable examples
• Expose a RocksDBKVStore interface that conforms to the MapStore interface
• Add documentation on how it can be used with the SMT
• Add runnable examples

Non-goals / Non-deliverables

• Change the existing MapStore interface
• Change any existing submodules
• Rewrite RocksDB - use an existing implementation

General deliverables

• Comments: Add/update TODOs and comments alongside the source code so it is easier to follow.
• Testing: Add new tests (unit/fuzz/benchmarks) to the test suite.
• Makefile: Add new targets to the Makefile to make the new functionality easier to use.
• Documentation: Update architectural or development READMEs; use mermaid diagrams where appropriate.

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Creator: @h5law

[h5law]

As a reference for future submodules: https://github.com/cosmos/cosmos-db

[okdas]

Very interesting page by erigon who currently are happy with MDBX - https://github.com/erigontech/erigon/wiki/Choice-of-storage-engine.