Use Paths rather than strings where possible

[oscargus]

Avoids quite a bit of conversions back and forth.

Also add some typing to make it easier to remember...

[oscargus]

The !s specifier is not required (unless a special case where one would like to override specifiers in the string). There are 200 or so remaining locations, but I changed where I saw them.

The cwd argument can be a Path. A bit unsure about the other arguments though, so still use strings there.

[oscargus]

Probably should do this in a more systematic way later, so closing.