set io_uring for rocksdb a default feature

this was already enabled by default by rocksdb technically, but
it wasn't building with it properly.

Signed-off-by: strawberry <strawberry@puppygock.gay>

Cargo.toml

@@ -362,6 +362,7 @@ default = [
     "brotli_compression",
     "zstd_compression",
     "release_max_log_level",
+    "io_uring",
 ]
 backend_sqlite = ["sqlite"]
 backend_rocksdb = ["rocksdb"]