Add KV store

[arriqaaq]

This is a draft PR for the KV store with a bunch of pending changes as listed below:

Store Changes

• Fix Range scans (scans don't stop at end bound)
• Remove dependency from VariableKey during scan reads
• Add hermitage tests for SSI
• Add Per KV checksum
• Fix options which are not implemented
• Add hermitage tests for SI
• Make BLOCK_SIZE = 32kb
• Add key reader (scan support) to track reading multiple keys in a transaction
• Add Read Cache
• Store all database options in file header
• Add close method to store
• Fix value reference decode
• Need to terminate keys when inserting to snapshot and index (Foo vs foo2 bug (bytes need to be appended with delimiter “\0” as in vector key for art to differentiate))
• Improve Store API (create vector/array key from byte array instead of making the user import Vector/Array key, and remove dependency on bytes::Bytes for txn api)