improvement: allow rocksdb again

Cargo.toml

@@ -78,6 +78,7 @@ crossbeam = { version = "0.8.1", optional = true }
 num_cpus = "1.13.0"
 threadpool = "1.8.1"
 heed = { git = "https://github.com/timokoesters/heed.git", rev = "f6f825da7fb2c758867e05ad973ef800a6fe1d5d", optional = true }
+rocksdb = { version = "0.16.0", features = ["multi-threaded-cf"], optional = true }
 thread_local = "1.1.3"
 # used for TURN server authentication
 hmac = "0.11.0"
@@ -87,7 +88,8 @@ sha-1 = "0.9.8"
 default = ["conduit_bin", "backend_sqlite"]
 backend_sled = ["sled"]
 backend_sqlite = ["sqlite"]
-backend_heed = ["heed", "crossbeam", "parking_lot"]
+backend_heed = ["heed", "crossbeam"]
+backend_rocksdb = ["rocksdb"]
 sqlite = ["rusqlite", "parking_lot", "crossbeam", "tokio/signal"]
 conduit_bin = [] # TODO: add rocket to this when it is optional