feat: add object iterator

[tdakkota]

Fixes #47

[codecov]

Codecov Report

Merging #48 (e8ccd63) into main (0a79161) will decrease coverage by 0.08%.
The diff coverage is 96.61%.

@@             Coverage Diff             @@
##              main      #48      +/-   ##
===========================================
- Coverage   100.00%   99.91%   -0.09%     
===========================================
  Files           36       37       +1     
  Lines         2323     2381      +58     
===========================================
+ Hits          2323     2379      +56     
- Misses           0        2       +2     

Impacted Files	Coverage Δ
dec_b64.go	100.00% <ø> (ø)
dec_obj_iter.go	96.55% <96.55%> (ø)
dec_arr_iter.go	100.00% <100.00%> (ø)

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