Blocking user from using optimize sign while casting the graph/ Removing constant folding flag from ptq

Small MR introducing a few corrections:

• Constant folding has been removed from the quantize_network() function and will soon be exposed independently via Pybind (Benjamin is currently working on this).

• Added an assert to ensure that users do not enable the optimizeSign flag when casting the graph. This feature will be available in upcoming PTQ merge requests.

• Updating the .gitignore file to exclude quantization_version.h