Add useful error messages/types to Result<T, ()>

There are multiple functions that return Result<T, ()> in the code, this is equivalent to Option<T>, however instead of changing those to optional types, these should return useful error messages/types so it's easier to debug.

Example: https://github.com/graphprotocol/graph-node/blob/79390c39a13f166999ceea8defc55eedd05265ab/graph/src/data/subgraph/mod.rs#L169

Some of them could just return &str/String but preferably they should return a proper error type or just an instance of anyhow. If for any of them you decide to create new error types, consider using the crate thiserror 🙂

If you never used any of these crates mentioned above, take a look at our codebase, you'll find usages of both. And if you're doing something outside of the graph crate/folder, you might want to import those from it's prelude module.

Commencez par graph/src/data/subgraph/mod.rs dans l’exemple lié, puis recherchez dans la base de code les fonctions qui renvoient Result<T, ()>. Examinez les utilisations existantes de anyhow et thiserror, et recensez les cas d’échec de chaque candidat avant de décider des messages ou des types d’erreur utiles. C’est terminé lorsque les résultats pertinents de type unit ne suppriment plus les informations d’erreur dans les chemins de code identifiés.