Initial AccountsDB implementation

[0xNineteen]

need the implement the basic functionality of accounts-db

• loading and indexing accounts from snapshot data
• verifying data correctness
• loading system accounts and sysvars

progress:

• deserialize snapshot metadata (accounts-db: initial implementation #40)
• load snapshot accounts (accounts-db: accounts files #42)
• account indexing (accounts-db: loading, indexing, validating accounts #54)
• loading sysvars (accounts-db: sysvar parsing #56)
• support incremental snapshots (accounts-db: support incremental snapshots #58)
• write accounts functionality
• setup rust-client benchmarking
• benchmark (reads, writes)
• disk-based indexing
• larger benchmarks (accounts stored on disk)
• disk-based indexing benchmarks
• improve disk-based indexing for reads
• improve hashmap performance
• improve snapshot loading
• re-run benchmarks (and improve upon rust client)
• more advanced benchmarks (multiple slot lists, larger initial accounts before benchmarking writes, ...)
• improve snapshot reading (.tar.zstd format is slow right now)
• improve memory allocations + fix leaks (current impl is inefficient right now + FBA sucks at free-ing memory)
• add additional account cleaning (/reclaims/swapping states which come from the same slot)
• snapshot downloads via gossip