Json prefix parameter

[HarelM]

This adds a json prefix option to allow parsing it back when needed.
Since objects are json.strigified, adding a prefix will allow finding where an object was stringified and parse it back to json.
This is a hack, but other alternatives are more complicated and I'm not sure are better.
In theory, when MLT will support nested properties we can remove this option.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.85%. Comparing base (9fda752) to head (12f9d57).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #28   +/-   ##
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  Coverage   98.85%   98.85%           
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  Files           3        3           
  Lines         174      175    +1     
  Branches       54       55    +1     
=======================================
+ Hits          172      173    +1     
  Misses          2        2           

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[HarelM]

CC: @wayofthefuture

[HarelM]

This is discusses as an option to solve:

• feat: support geojson nested objects maplibre-gl-js#6992

It's a lot simpler than the other options I tried.

[mwilsnd]

Looks reasonable to me, agreed this should be revisited once MVT matures.