Fields are implicitly converted to number when saving json

[R-omk]

Unlike msgpack, json cannot contain anything other than strings in keys.
I believe that it should always save strings. For other cases, make some exceptions explicitly.

[R-omk]

One option is to use explicit types with yaml instead of json, moreover yaml is more human-readable.

obj:
  txt: some1
  !!str 2: some2

Yaml from symfony already support !!str and !!float but not support !!int https://symfony.com/doc/current/components/yaml/yaml_format.html#unsupported-yaml-features