chore: Move rest of coloring.rs into secret-memory crate

Also removes the StoreSecret trait from cli.rs as it was
redundant.

secret-memory/src/file.rs

@@ -0,0 +1,7 @@
+use std::path::Path;
+
+pub trait StoreSecret {
+    type Error;
+
+    fn store_secret<P: AsRef<Path>>(&self, path: P) -> Result<(), Self::Error>;
+}