gpui: Relax AssetLogger trait bounds

[tidely]

Loosen trait bounds from std::error::Error to std::fmt::Display, since it's not required for the log::error! macro or any other bounds.

Specify that AssetLogger specifically logs errors in its documentation.

Use the futures::TryFutureExt trait extension to use inspect_err directly on a future.

Release Notes:

• N/A

[mikayla-maki]

Thanks!