Production RocksDB State and Block Persistence

[Steake]

Part of Epic: #74 - RC2: Production Network & Storage

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Goal: Expand from basic block/state persistence to include index, snapshots, pruning, atomic writes for production.

Requirements:

• Store blocks by height/hash, headers in separate column family
• Account data, state root, fast range queries
• Transaction index (hash, sender, O(1) lookup)
• Snapshots and pruning functionality added

Acceptance Criteria:

• All persistence and recovery flows tested and benchmarked
• 3-node testnet runs 1+ week with no state loss

See [RELEASE_REQUIREMENTS.md](https://github. com/Steake/BitCell/blob/master/docs/RELEASE_REQUIREMENTS.md)

[Steake]

[autopilot] @copilot please start work on this issue and open a PR that references #52 in the PR description.