feat: ArgumentComsumer return result with err

[smuu]

Description

With the ability to return errors with the ArgumentConsumer, we can provide proper feedback to the command sender.
For example, when specifying an invalid player, we can provide a proper message instead of sending a message that the command syntax is incorrect.

Testing

Checklist

Things need to be done before this Pull Request can be merged.

• Code is well-formatted and adheres to project style guidelines: cargo fmt
• Code does not produce any clippy warnings: cargo clippy
• All unit tests pass: cargo test
• I added new unit tests, so other people don't accidentally break my code by changing other parts of the codebase. How?

[Snowiiii]

Found out that /gamemode invalid_gamemode and an empty player (e.g. /kill does produce and "Internal Error"

[smuu]

Thinking about this again, we don't need this (yet)