Adopt `System.OsPath.OsPath` from `filepath >= 1.4.100.0`

[mpilgrem]

Stack currently uses type FilePath = String (as well as the types from package path). The authors of filepath-1.4.100.0 recommend OsPath over FilePath as being 'more correct'.

GHC comes with filepath. For GHC 9.4.2, that is filepath-1.4.2.2.

directory-1.3.8.0 depends on filepath >= 1.4.100.0. fast-logger-3.1.1 depends on directory. However, it won't build with directory-1.3.8.0 because its modules are no longer safe - see kazu-yamamoto/logger#204.