= Electrum
Update height to -1 for txns with any unconfirmed input (https://electrumx.readthedocs.io/en/latest/protocol-basics.html#status)
Snapshot DB after successful indexing - and run queries on this snapshot
Handle multiple RPC client in parallel
Figure out graceful shutting down RPC server

= Bitcoind
Handle bitcoind connection failures - instead of crashing
Use p2p protocol for querying blocks - similar to `bitcoincore-indexd`
Lookup confirmed transactions only at their blocks (using `blockhash` parameter of `getrawtransaction` RPC), so -txindex won't be needed
Add getrawtransactions() API (for RPC batching)

= Performance
Add timing/profiler helpers (for indexing/DB/RPC operations)
Measure first-time query latency
Flush only on the last write.

= Rust
Use Bytes instead of Vec[u8] when possible
Return errors instead of panics
Use generators instead of vectors