Redb slasher backend impl (#4529)

* initial redb impl

* redb impl

* remove phantom data

* fixed table definition

* fighting the borrow checker

* a rough draft that doesnt cause lifetime issues

* refactoring

* refactor

* refactor

* passing unit tests

* refactor

* refactor

* refactor

* commit

* move everything to one database

* remove panics, ready for a review

* merge

* a working redb impl

* passing a ref of txn to cursor

* this tries to create a second write transaction when initializing cursor. breaks everything

* Use 2 lifetimes and subtyping

Also fixes a bug in last_key caused by rev and next_back cancelling out

* Move table into cursor

* Merge remote-tracking branch 'origin/unstable' into redb-slasher-backend-impl

* changes based on feedback

* update lmdb

* fix lifetime issues

* moving everything from Cursor to Transaction

* update

* upgrade to redb 2.0

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into redb-slasher-backend-impl

* bring back cursor

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into redb-slasher-backend-impl

* fix delete while

* linting

* linting

* switch to lmdb

* update redb to v2.1

* build fixes, remove unwrap or default

* another build error

* hopefully this is the last build error

* fmt

* cargo.toml

* fix mdbx

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into redb-slasher-backend-impl

* Remove a collect

* Merge remote-tracking branch 'origin/unstable' into redb-slasher-backend-impl

* Merge branch 'redb-slasher-backend-impl' of https://github.com/eserilev/lighthouse into redb-slasher-backend-impl

* re-enable test

* fix failing slasher test

* Merge remote-tracking branch 'origin/unstable' into redb-slasher-backend-impl

* Rename DB file to `slasher.redb`

slasher/src/database/lmdb_impl.rs

@@ -100,7 +100,7 @@ impl Environment {
 impl<'env> RwTransaction<'env> {
     pub fn get<K: AsRef<[u8]> + ?Sized>(
         &'env self,
-        db: &Database<'env>,
+        db: &'env Database,
         key: &K,
     ) -> Result<Option<Cow<'env, [u8]>>, Error> {
         Ok(self.txn.get(db.db, key).optional()?.map(Cow::Borrowed))
@@ -182,6 +182,29 @@ impl<'env> Cursor<'env> {
             .put(&key, &value, RwTransaction::write_flags())?;
         Ok(())
     }
+
+    pub fn delete_while(
+        &mut self,
+        f: impl Fn(&[u8]) -> Result<bool, Error>,
+    ) -> Result<Vec<Cow<'_, [u8]>>, Error> {
+        let mut result = vec![];
+
+        loop {
+            let (key_bytes, value) = self.get_current()?.ok_or(Error::MissingKey)?;
+
+            if f(&key_bytes)? {
+                result.push(value);
+                self.delete_current()?;
+                if self.next_key()?.is_none() {
+                    break;
+                }
+            } else {
+                break;
+            }
+        }
+
+        Ok(result)
+    }
 }
 
 /// Mix-in trait for loading values from LMDB that may or may not exist.