[Modes] Adding a getDeviceCount API to query number of available devices in an enabled mode

[noelchalmers]

Description

[codecov]

Codecov Report

Merging #427 (b011a96) into main (6c98e86) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #427      +/-   ##
==========================================
- Coverage   76.24%   76.21%   -0.04%     
==========================================
  Files         242      242              
  Lines       18790    18802      +12     
==========================================
+ Hits        14327    14330       +3     
- Misses       4463     4472       +9     

Impacted Files	Coverage Δ
src/modes.cpp	87.71% <0.00%> (-8.44%)	⬇️
src/modes/openmp/registration.cpp	77.77% <0.00%> (-22.23%)	⬇️
src/modes/serial/registration.cpp	94.11% <0.00%> (-3.85%)	⬇️
src/lang/specialMacros.cpp	59.48% <0.00%> (ø)
src/tools/sys.cpp	65.39% <0.00%> (+0.24%)	⬆️

[dmed256]