Current HEAD of NNVC cannot compile when `NN_POST_FILTERING` is set to 0.

Description of the issue

The current HEAD of NNVC cannot compile when NN_POST_FILTERING is set to 0.

Additional information

This issue is observed using GCC-13.1.1. It is also observed using MSVC.

When NN_POST_FILTERING is set to 0, the compilation of the current HEAD of NNVC faces two separate issues.

(1) The structure Fraction is not defined while being used, see "source/Lib/CommonLib/TypeDef.h".

(2) "DecLib::executePostFilter()" is defined but not declared, see "source/Lib/DecLib/DecLib.cpp" and "source/Lib/DecLib/DecLib.h".