feat(discord): Moved most strings to Strings

- Added Error::AccountIsSelf variant
- /balance give to self now returns error

discord/src/error.rs

@@ -15,6 +15,7 @@ pub enum Error {
     SerenityError(serenity::Error),
     SquadQuestError(squad_quest::error::Error),
     AccountNotFound,
+    AccountIsSelf,
     InsufficientFunds(u32),
     RoomNotFound(u16),
     RoomAlreadyUnlocked(u16),
@@ -57,6 +58,7 @@ impl Display for Error {
             Self::SerenityError(_) => write!(f, "discord interaction error"),
             Self::SquadQuestError(_) => write!(f, "internal logic error"),
             Self::AccountNotFound => write!(f, "account not found"),
+            Self::AccountIsSelf => write!(f, "given account is the same as command user"),
             Self::InsufficientFunds(amount) => write!(f, "user does not have {amount} points"),
             Self::RoomNotFound(id) => write!(f, "room #{id} not found"),
             Self::RoomAlreadyUnlocked(id) => write!(f, "room #{id} is already unlocked for this user"),
@@ -75,6 +77,7 @@ impl std::error::Error for Error {
             Self::NoChannelOrUser |
             Self::BothChannelAndUser |
             Self::AccountNotFound |
+            Self::AccountIsSelf |
             Self::InsufficientFunds(_) |
             Self::RoomNotFound(_) |
             Self::RoomAlreadyUnlocked(_) |