[enchancement] Add Path Validations to Environment Variables

[newtoallofthis123]

This is a proposal to add path based validations to the environ.rs files in both swhks and swhkd as suggested by @zubairmh in #243 (comment).

This can achieved by adding a new Error enum and also handling it: If the directory path doesn't exist, the defaults can be used.
There is a case for creating the directories on the fly, so am not sure yet 😄