Dependency updates for conda package

I tried installing the dnadna package with mamba and it mostly worked fine modulo a couple issues, that I think were not specific to mamba:

• The version of msprime we're using has its extension module linked explicitly to libopenblas; most of our dependencies are using MKL by default (this is an endemic issue with conda packages--selecting the right BLAS). But msprime is explicitly built against libopenblas. So we must include that as a dependency, it seems.

• In newer versions of pytorch, it seems torch.utils.tensorboard explicitly requires tensorboard to already be installed when it's imported. IIRC this was not previously the case. But we should account for this. I think tensorboard should be kept as an optional dependency since it adds a bit of overhead, but we can add a clear warning in the logs about it if it's missing.