run() without pyvista leads to an unecessary warning

[koubaa]

using run() without pyvista leads to warning messages

mapdl.run("!comment")
/home/staff/mkoubaa/sites/site4/ansys/mapdl/core/misc.py:1024: UserWarning: To use the method 'geometry', the package 'pyvista' is required.
Please try to install 'pyvista' with:
pip install pyvista
  warn(msg)

 /OUTPUT FILE= anstmp

The reason appears to be the _reset_cache() function in mapdl_grpc.py reads from the mapdl.geometry property which tries to construct a Geometry object that depends on pyvista. I think it can be fixed by mapdl_grpc.py holding a member variable for that is initailized to None and used by the geometry property on first access.