refactor: Rewrite cmd_duration, directory and env_var module to use module config (#460)

This PR is a batched rewrite of the following modules:
- cmd_duration
- directory
- env_var

src/configs/mod.rs

@@ -1,8 +1,11 @@
 pub mod aws;
 pub mod battery;
 pub mod character;
+pub mod cmd_duration;
 pub mod conda;
+pub mod directory;
 pub mod dotnet;
+pub mod env_var;
 pub mod go;
 pub mod hostname;
 pub mod jobs;