Add support for NATIVE_SIZE=128 in OpenFHE

[sloede]

As discussed today, it would be great if a user could choose whether to use the OpenFHE library with 64 bit or 128 bit native size as the backend. The default should remain as it is now (64 bit), and the 128 bit version should be selectable through a compile-time preference using Preferences.jl, e.g., by setting NATIVE_SIZE to either 64 or 128.

After thinking about about our discussion today, I believe we should make this available to users no matter what the conclusions about its usability for our cases says. That is, let's create this anyways :-)

Feel free to let me know in case of questions regarding how to implement this in Yggdrasil or with the preferences.