migrate from conda to micromamba

micromamba is a simple binary and easier to install on systems. It's also fast for installs than traditional conda. In addition, on the HPC where conda will by default download packages in ~/.conda we can set the root-prefix in micromamba to $SCRATCH or somewhere that won't impact our quota. 

```
Prefix options:
  -r,     --root-prefix PATH  Path to the root prefix 
```