For legacy mode:
1. For mutate commands, an empty result should throw an error
2. For read commands, it returns nil if path was not found, but if it was matched
but only with a wrong types, it will throw an error.
For non-legacy mode, objlen should throw an error for non existing key.
Simplified JsonCallbackResult a bit and made sure more fakeredis tests are passing.
Signed-off-by: Roman Gershman <roman@dragonflydb.io>
feat: a test with flat buffers
Also, add an experimental flag `--experimental_flat_json` that allows writing json objects as flat strings using
flexibuffers.
The experiment shows that `debug populate 100000 a 10 type json elements 30`
uses almost 3 times less memory than with native jsoncons objects.
Signed-off-by: Roman Gershman <roman@dragonflydb.io>
