* add cache clearing for oh-my-posh package changes
Using oh-my-posh creates script files in `~/.cache/oh-my-posh` which include an old derivation path. Once that path is garbage collected, oh-my-posh stops working preventing to successfully create new shells.
```
bash: /nix/store/5ddhz8nsahf1d03smzx2xpmynjspjfh8-oh-my-posh-26.8.0/bin/oh-my-posh: No such file or directory
```
* fix oh-my-posh package reference in cache clear
Use the configured value from programs.oh-my-posh.package as the value of oh-my-posh to compare during cache cleanup.
0c7c71a212