Fix NaN in JSON Feature

[ilkilic]

• Fix NaN values in JSON
• Ensure 'current' array operations use float64 to prevent casting error
• Refactor sAHP unit test
• Add APThreshold unit test

[codecov-commenter]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (0ae5960) 71.35% compared to head (d799ed0) 73.94%.

Files	Patch %	Lines
bluepyefe/ecode/DeHyperPol.py	0.00%	3 Missing ⚠️
bluepyefe/ecode/HyperDePol.py	0.00%	3 Missing ⚠️
bluepyefe/ecode/SpikeRec.py	0.00%	3 Missing ⚠️
bluepyefe/ecode/negCheops.py	0.00%	1 Missing ⚠️
bluepyefe/ecode/posCheops.py	0.00%	1 Missing ⚠️
tests/ecode/test_apthresh.py	98.14%	1 Missing ⚠️
tests/ecode/test_sahp.py	98.18%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #169      +/-   ##
==========================================
+ Coverage   71.35%   73.94%   +2.58%     
==========================================
  Files          36       38       +2     
  Lines        2304     2391      +87     
==========================================
+ Hits         1644     1768     +124     
+ Misses        660      623      -37     

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[AurelienJaquier]

Looks good to me, thanks @ilkilic