return of the iter method

[cel055]

the return of the iter method on the state store now returns an iterator

[codecov]

Codecov Report

Merging #264 (6092950) into master (4833a3c) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #264      +/-   ##
==========================================
- Coverage   78.73%   78.70%   -0.03%     
==========================================
  Files          22       22              
  Lines        1919     1921       +2     
==========================================
+ Hits         1511     1512       +1     
- Misses        408      409       +1     

Files	Coverage Δ
cognite/extractorutils/__init__.py	100.00% <100.00%> (ø)
cognite/extractorutils/statestore.py	91.35% <100.00%> (ø)

... and 2 files with indirect coverage changes