Add hash → block number index + lookup API

[mo4islona]

Summary

Lets consumers resolve a bare block hash to its block number. Today the hash is only buried inside each chunk's Arrow hash column, so the only way to look it up is a linear scan (~0.1–0.6s, and worse as retention grows). This adds a proper index for an O(1) point lookup, plus an HTTP endpoint to use it.

The motivation: services that receive a raw hash (from logs, fork events, external sources) need to map it back to a block number to keep working with the standard /stream APIs.

What's new

• Storage — a RocksDB index mapping hash → block number per dataset, kept up to date automatically as chunks are ingested, forked, and pruned. Enabled for EVM datasets for now (easy to extend to other chains later).
• Hotblocks — GET /datasets/{id}/hashes/{hash}/block, returning {number, hash} or 404 if the hash isn't found.

Rollout notes

• No backfill: the index covers only data ingested after this ships. Hashes from chunks that already exist at upgrade time resolve to 404 until those chunks roll off via retention. Worth calling out in release notes.
• Safe to roll back: older binaries simply ignore the new column family.

Testing

Unit tests in sqd-storage cover ingest, fork, retention, dataset deletion, and confirm compaction leaves the index intact. Manual HTTP smoke against a live hotblocks instance still recommended.

🤖 Generated with Claude Code

[elina-chertova]

Heads-up: dogfooding this branch as data-hotblocks:pr-72 is degrading a shared hotblocks instance

The pr-72 build of this branch has been running on the network-hotblocks-mainnet-internal hotblocks-db since ~2026-06-03, and it has been progressively degrading every dataset on that instance (not just EVM ones):

• Processing time (head_monitor_result_ms_last, 3h) spikes across all datasets together — solana-mainnet 404 s, berachain 103 s, linea 94 s, ethereum-mainnet 92 s — while the same datasets on the public deployment (image b5b8886, i.e. without this branch) stay <500 ms.
• Downstream this trips Portal_Hotblocks_Data_Lag_Critical / Avg_Processing_Time_High for solana-mainnet, solana-devnet and hyperliquid-fills (see subsquid/infra#544).

Why non-EVM datasets are hit by an EVM-only feature: index_block_hashes() (added to insert_chunk/insert_fork in write/dataset_update.rs + write/tx.rs) runs inline inside the ingest transaction and, for every EVM chunk, iterates every block's hash into CF_BLOCK_HASHES via self.transaction.put_cf. Even though is_indexed_kind short-circuits non-EVM datasets, the ~25 EVM datasets' extra per-chunk index writes + the new column family's compaction contend on the shared RocksDB instance, starving the highest-throughput consumers (solana most of all). The pressure grows with retention, which is why it took weeks to become alert-worthy.

Not asking to change the feature's design — just flagging that before this ships to a shared multi-dataset instance, the hash indexing likely needs to move off the synchronous ingest path (background/async index maintenance) or otherwise be prevented from contending with unrelated datasets' ingestion. Immediate mitigation is rolling the internal image back to b5b8886 (subsquid/infra#544).