Update data check and add deg2rad & rad2deg

[GidonFrischkorn]

Summary

Tests

[x] Confirm that all tests passed
[x] Confirm that devtools::check() produces no errors

Release notes

• Add deg2rad & rad2deg functions
• Only throw warning for VWM models if values larger than 2pi are detected for the response variable

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (e2c1fc0) 65.84% compared to head (37cc6c0) 65.80%.
Report is 2 commits behind head on develop.

Files	Patch %	Lines
R/helpers-data.R	70.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #74      +/-   ##
===========================================
- Coverage    65.84%   65.80%   -0.04%     
===========================================
  Files           16       16              
  Lines          969      971       +2     
===========================================
+ Hits           638      639       +1     
- Misses         331      332       +1     

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[venpopov]

I added this line to the warning:

The model requires the response variable to be in radians.\n

so that users don't wonder what to do