feat(storage): add EitherReader for routing history queries to MDBX or RocksDB

[yongkangc]

Summary

Adds EitherReader abstraction to route historical state queries (account history, storage history) to either MDBX or RocksDB based on storage settings. This is the foundation for using RocksDB as an alternative backend for history indices.

Changes

EitherReader Abstraction

• Add EitherReader enum with Database and RocksDB variants in either_writer.rs
• Implement account_history_info() and storage_history_info() methods that handle shard lookups
• Extract shared compute_history_rank() and needs_prev_shard_check() helpers to reduce duplication between backends

Historical State Provider Integration

• Wire EitherReader into HistoricalStateProviderRef for account and storage lookups
• Add with_rocksdb_tx() helper to RocksDBProviderFactory trait for scoped RocksDB transactions

RocksDB Provider Enhancements

• Add history_info() method to RocksTx for efficient shard lookups using raw iterators
• Implement proper shard logic for history indices in write_blocks_data
• Handle sentinel-only entries and empty tables in consistency checks

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PR Stack

main
  ↑
#21063 (rocksdb-either-reader) ◀ you are here
  ↑
#21124 (rocksdb-index-account-history)
  ↑
#21125 (rocksdb-index-storage-history)

• feat(storage): add EitherReader for routing history queries to MDBX or RocksDB #21063 ◀
• feat(stages): add RocksDB support for account history index stage #21124
• feat(stages): add RocksDB support for storage history index stage #21125

[gakonst]

Code Review: PR #21063 (Base of RocksDB stack)

CI Status

• ❌ clippy failure
• ❌ udeps failure
• ❌ test / ethereum / edge failure

Changes Summary

Adds EitherReader abstraction to route history lookups to MDBX or RocksDB based on storage settings. Good design pattern.

Review Notes

✅ Good

• Clean abstraction with EitherReader enum variants
• with_rocksdb_tx helper nicely encapsulates cfg-gated code
• Proper rank/select logic for history lookups
• needs_prev_shard_check reused correctly

🟡 Suggestions

1. Duplicated rank/select logic: The rank adjustment code is duplicated in both account_history_info and storage_history_info:

   let mut rank = chunk.rank(block_number);
   if rank.checked_sub(1).and_then(|r| chunk.select(r)) == Some(block_number) {
       rank -= 1;
   }
   let found_block = chunk.select(rank);

   Consider extracting to a helper function (I see #21064 adds compute_history_rank - good).

2. Test pattern match update: Line 1032 updates to EitherReader::Database(_) but line 1027 still has EitherReader::StaticFile(_, _) - inconsistent pattern. Should be StaticFile(..) for consistency with other changes.

3. PhantomData inconsistency: StaticFile variant keeps PhantomData<&'a ()> but comment says it's for lifetime when rocksdb feature is disabled. The Database variant no longer has it - verify this compiles correctly with all feature combinations.

Blocking Issues

Fix CI failures before this can be merged - likely clippy warnings and unused deps.

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Review by @tempo_ai

[yongkangc]

but i think we have to turn the with_rocksdb_tx/batch and the batch we pass to the eihereader an option, otherwise we'll always be creating it even for legacy nodes