feat(rust): make JSON serialization of DataType and Field public

[wjones127]

No description provided.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.95%. Comparing base (6101528) to head (7c0aaef).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3161      +/-   ##
==========================================
- Coverage   77.96%   77.95%   -0.02%     
==========================================
  Files         242      242              
  Lines       82455    82455              
  Branches    82455    82455              
==========================================
- Hits        64290    64274      -16     
  Misses      14978    14978              
- Partials     3187     3203      +16     

Flag	Coverage Δ
unittests	77.95% <100.00%> (-0.02%)	⬇️

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[albertlockett]

very nice!