Reduce max modeMemory usage of modeMemoryPool_t::resize

[stgeke]

The current implementation uses 'modeMemory' for both the new and old pool. While this method allows for fast data copying, it also results in high memory usage. This can be tricky in cases where we're running short on device memory. We might want to think about adding an option to stage it through to lower the maximum memory usage.

[kris-rowe]

We will upstream an option to reallocate through host-memory from nekRS that addresses this.