feat(rollup): persist block hash and resume via set_with_head

[temrjan]

What

Adds a hash column to the block table so the rollup can record the hash of every block it processes. On startup, a new Database::highest_block reads the latest persisted (number, hash) and Rollup::new calls ExExNotificationsStream::set_with_head with it — reth backfills any L1 blocks committed while the rollup was offline.

Why — and fixes two pre-existing bugs

1. reth_revm::Database::block_hash was unusable. It selected a hash column from block, but the schema never had one. Any EVM execution touching the BLOCKHASH opcode would crash on startup. The new column makes the trait method actually work.

2. ORDER BY number DESC sorted lexicographically. number is TEXT, so "9" ranked above "10". Both Database::highest_block (new) and Database::revert_tip_block (pre-existing) now use ORDER BY CAST(number AS INTEGER) DESC. A regression test guards it.

This is the rollup half of #25; op-bridge half is in #59.

Migration note

Schema changed — delete any existing rollup.db before running this version. The previously committed rollup.db fixture is removed as part of this change.

Testing

• cargo build -p rollup
• cargo test -p rollup — 4 passed (was 1; added: empty DB, latest persisted, numeric ordering regression)
• cargo clippy -p rollup --all-targets --all-features -- -Dwarnings
• cargo +nightly fmt --all --check
• cargo +nightly doc -p rollup --all-features --no-deps --document-private-items with RUSTDOCFLAGS="-D warnings"

@mattsse happy to adjust the schema migration approach (currently relies on "delete old DB") or the location of the set_with_head call if you'd prefer a different design.

Refs: #25