Standardize to lower-case for all dictionary keys

[Sparks29032]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.93%. Comparing base (fc45fa1) to head (d1339f6).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #307   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          24       24           
  Lines        1480     1570   +90     
=======================================
+ Hits         1479     1569   +90     
  Misses          1        1           

Files with missing lines	Coverage Δ
tests/test_morphapp.py	100.00% <100.00%> (ø)
tests/test_morphio.py	100.00% <100.00%> (ø)
tests/test_morphpy.py	100.00% <ø> (ø)

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