feat: Start dummy in-memory database

src/db/user.rs

@@ -0,0 +1,37 @@
+use std::fmt;
+
+#[derive(Clone, Debug)]
+pub struct UserRef {
+    pub username: String,
+    pub domain: String,
+}
+
+impl fmt::Display for UserRef {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}@{}", self.username, self.domain)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct User {
+    pub username: String,
+    pub domain: String,
+    pub password: String,
+    pub mail: String,
+    // recovery_mail: String,
+}
+
+impl User {
+    pub fn user_ref(&self) -> UserRef {
+        UserRef {
+            username: self.username.clone(),
+            domain: self.domain.clone(),
+        }
+    }
+}
+
+impl fmt::Display for User {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}@{}", self.username, self.domain)
+    }
+}