Slasher redb upgrade

[owanikin]

Issue Address

#8048

Started addressing the Slasher database migration requirement for Redb as discussed.

Proposed Changes

• Added upgrade() support for Redb in slasher/src/database/redb_impl.rs.
• Integrated upgrade() into slasher/src/database/interface.rs.
• Incremented schema version for Redb backend.
• Handled upgrade/downgrade logic in slasher/src/migrate.rs.
• Fixed clippy issues

Additional Info

• Tested locally with Holesky by running Lighthouse beacon node + Slasher using Redb. I am having issues here, as I think I am not testing it properly. Will request advice from @eserilev

[eserilev]

Thanks! I took a brief look and requested some changes

also the match(schema_version, CURRENT_SCHEMA_VERSION) has some cases that look a bit weird to me, I'll take a deeper look once we've cleaned this PR up a bit.

[eserilev]

should this function be upgrading the db?

[owanikin]

Right now, this upgrade() in redb_impl.rs is just a backend hook.
The actual schema version check and upgrade orchestration happens in slasher/src/migrate.rs (via SlasherDB::migrate), which calls self.env.upgrade() and then writes the new schema version into the metadata_db.

For Redb specifically, there aren’t any low-level internal migrations needed at the moment, so this is effectively a no-op.
I left the function in place so the Redb backend matches the Environment interface and can support backend-specific migrations in the future if needed.