How could this have been working until now?
We should not call `cudaFree` on uninitialized memory.

We have to free the old pointers before resize. This also prevents
memory leakage in case the vector gets shrinked.

Apparently the previous code relied on the fact that `resize` somehow
initialized the memory to null pointers or that `cudaFree` just ignores
pointers it didn't allocate.

lbmpy Code Generation Tutorials

See merge request !330

Bugfix: Guo force model for non-SRT

See merge request !332

Update find boost

See merge request walberla/walberla!331

Resolve "Some tests are very slow in coverage job"

Closes #127

See merge request !327

Code Generation for PDEs tutorial

See merge request walberla/walberla!326