[Mig] storage to SQLite pool

[Clean] split message handler dispatch

iota-storage/src/storage_error.rs

@@ -0,0 +1,13 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum StorageError {
+    #[error("Database error: {0}")]
+    Db(#[from] rusqlite::Error),
+    #[error("Connection pool error: {0}")]
+    Pool(String),
+    #[error("IO error: {0}")]
+    Io(#[from] std::io::Error),
+    #[error("{0}")]
+    Other(String),
+}