Add MYPY_CACHE_DIR to sweep mypy caching under the rug

dotfiles/config/bashum/main.bashrc

 export MDVIMB__CONVERTER=cmark
 export MDVIMB__STYLE=darkzen    # pergamen
 
+export MYPY_CACHE_DIR="$HOME/.cache/mypy/the_darn_cache"
+
 #shellcheck disable=SC2034
 {
     GIT_PS1_SHOWDIRTYSTATE=true