Error typing for rustical_store as well as some refactoring

crates/store/src/error.rs

@@ -0,0 +1,23 @@
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("Not found")]
+    NotFound,
+
+    #[error(transparent)]
+    SqlxError(sqlx::Error),
+
+    #[error(transparent)]
+    Other(#[from] anyhow::Error),
+
+    #[error(transparent)]
+    ParserError(#[from] ical::parser::ParserError),
+}
+
+impl From<sqlx::Error> for Error {
+    fn from(value: sqlx::Error) -> Self {
+        match value {
+            sqlx::Error::RowNotFound => Error::NotFound,
+            err => Error::SqlxError(err),
+        }
+    }
+}