Cache the collected gauge and clover fields when doing split grid

[hummingtree]

One could cache the collected gauge and clover fields and reuse the previously generated fields when doing split grid. The starting point should probably be

• https://github.com/lattice/quda/blob/ed21580eabd7dd8bfebee40a65ab813af1453f95/lib/interface_quda.cpp#L3180
• https://github.com/lattice/quda/blob/ed21580eabd7dd8bfebee40a65ab813af1453f95/lib/interface_quda.cpp#L3202

In order to do so, one needs

• A logic to determine if the previously generated field can be used.
• Then putting the cached field into a container somewhere for reusing.