Using `systemd.services.<name>.script` pulls in bash in the ExecStart
line for a service. Since our "script" was only one line anyways,
we can inline it to just use ExecStart directly. Losing shell features
shouldn't be detrimental here, as we're not using pipes and there are
no globs to expand.
adds the optional attribute `phys` to uniquely identify a single device, if multiple
devices share the same name
nixos/evremap: fix toml config generation
filter out attrsets with a `null` value as toml doesn't support it
nixos/evremap: use nixfmt
nixos/evremap: incorporate changes from review
