✨ feat(error): enhance error handling for configuration issues

- add specific error variants for unset directory, home expansion failure, and directory creation failure
- improve error reporting by providing more context in error messages

src/error.rs

@@ -3,10 +3,23 @@ use thiserror::Error;
 /// Error messages for cull-gmail
 #[derive(Debug, Error)]
 pub enum Error {
+    /// Configuration directory not set
+    #[error("Configuration directory not set")]
+    DirectoryUnset,
+    /// Expansion of home directory in `{0}` failed
+    #[error("Expansion of home directory in `{0}` failed")]
+    HomeExpansionFailed(String),
+    /// Directory creation failed for `{0}`
+    #[error("Directory creation failed for `{0:?}`")]
+    DirectoryCreationFailed((String, Box<std::io::Error>)),
     /// Error from the google_gmail1 crate
-    #[error("Google Gmail1 says: {0}")]
-    GoogleGmail1(#[from] google_gmail1::Error),
-    /// Error from the google_clis_common crate
-    #[error("Google CLIs Common says: {0}")]
-    InvalidOptionsError(google_clis_common::CLIError, i16),
+    // #[error("Google Gmail1 says: {0}")]
+    #[error(transparent)]
+    GoogleGmail1(#[from] Box<google_gmail1::Error>),
+    // /// Error from the google_clis_common crate
+    // #[error("Google CLIs Common says: {0}")]
+    // InvalidOptionsError(google_clis_common::CLIError, i16),
+    // /// Other error
+    // #[error("Error reported: {0}")]
+    // Other(#[from] String),
 }