When using a really big tree sequence, the reparam model runs out of memory since we're using [a matrix of number of internal nodes squared.](https://github.com/awohns/tspyro/blob/9bfcfc047c1329f6920beb82fc8e8b3de9148c70/tspyro/models.py#L252)
When using a really big tree sequence, the reparam model runs out of memory since we're using a matrix of number of internal nodes squared.