chore: meta mock test (#379)

* chore: meta mock

* chore: refacor datanode selector

* chore: create route mock test

* chore: add mock module

* chore: memory store for test

* chore: mock meta for test

* chore: ensure memorysotre has the same behavious with etcd

* chore: replace tokio lock to parking_lot

src/api/greptime/v1/meta/store.proto

@@ -47,6 +47,7 @@ message RangeResponse {
   
   // kvs is the list of key-value pairs matched by the range request.
   repeated KeyValue kvs = 2;
+  // more indicates if there are more keys to return in the requested range.
   bool more = 3;
 }