When `RM_ZsetAdd()`/`RM_ZsetIncrby()`/`RM_StreamAdd()` fails, if a new key happens to
be created using `moduleCreateEmptyKey()`, we should clean up the empty key.
## Test
1) Add new module commands(`zset.add` and `zset.incrby`) to cover `RM_ZsetAdd()`/`RM_ZsetIncrby()`.
2) Add a large-memory test to cover `RM_StreamAdd()`.