Introduce training mode switch to Dropout layer

[aobolensk]

On inference DropOut is normally no-op (unless specified explicitly). Introduce the training-mode parameter to control DropOut behavior

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.33%. Comparing base (2a2b9df) to head (bc8b106).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
include/layers/DropOutLayer.hpp	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #229      +/-   ##
==========================================
+ Coverage   83.84%   84.33%   +0.49%     
==========================================
  Files          44       44              
  Lines        2655     2770     +115     
  Branches     1466     1540      +74     
==========================================
+ Hits         2226     2336     +110     
  Misses        219      219              
- Partials      210      215       +5     

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