Refactor: Remove sledstore as a storage backend

The `sled` DB has known issues with memory and disk space management.
Even under relatively low load, it exhibits abnormal memory and disk
usage.

As a result, `sledstore` has been removed and is no longer recommended
as a storage backend.

.github/workflows/ci.yaml

@@ -145,7 +145,6 @@ jobs:
         include:
           - store: "stores/memstore"
           - store: "stores/rocksstore"
-          - store: "stores/sledstore"
 
     steps:
       - name: Setup | Checkout

Cargo.toml

@@ -61,7 +61,6 @@ members = [
     "tests",
     "stores/memstore",
     "stores/rocksstore",
-    "stores/sledstore",
 ]
 exclude = [
     "cluster_benchmark",

Makefile

@@ -74,7 +74,7 @@ unused_dep:
 
 typos:
 	# cargo install typos-cli
-	typos --write-changes openraft/ tests/ stores/memstore/ stores/rocksstore stores/sledstore examples/raft-kv-memstore/ examples/raft-kv-rocksdb/
+	typos --write-changes openraft/ tests/ stores/memstore/ stores/rocksstore examples/raft-kv-memstore/ examples/raft-kv-rocksdb/
 	#typos --write-changes --exclude change-log/ --exclude change-log.md --exclude derived-from-async-raft.md
 	# typos