replace OkayWAL with our own WAL implementation

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https://github.com/rdaum/moor/blob/47435a1442a1f5532c23944029e90982baa99bff/crates/db/src/rdb/paging/cold_storage.rs#L15

// this program. If not, see <https://www.gnu.org/licenses/>.
//

//! TODO: replace OkayWAL with our own WAL implementation

use std::collections::{HashMap, HashSet};
use std::path::PathBuf;