feat: cache block hashes

[onbjerg]

Caches block hashes, but also computes a block hash based on the block number if no block hash was returned from the underlying database.

Retrieving block hashes can be expensive (as is the case with our forking backend in Foundry), but it is also important that block hashes for different blocks differ from each other

@draganrakita I was unsure where to put this - we need it for cheats.roll to work correctly in Foundry, but it would also be weird to have a set_block_hash function in the database trait.

Two alternatives I could think of:

• Allow inspectors to override block hashes
• Implement our own database in Foundry, although this would pretty much be a 1:1 copy of CacheDB here with this patch

Curious to hear what you think

[rakita]

Having cached hashes seems okay, having custom hash created on H256::zero() seems like that it can be added to ExtDB for CacheDB feels like a small pitfall.

[gakonst]

@rakita Agree that doing on CacheDB seems weird. What about doing it on EmptyDB's fn block_hash? When we're forking, we're gonna have a value that corresponds to the number, but when we're not forking we're using EmptyDB, so maybe that's the right place for this logic. @onbjerg https://github.com/bluealloy/revm/blob/main/crates/revm/src/db/in_memory_db.rs#L206