fix(spells): allow empty args for callbackSrv [NET-651]

[justprosh]

Description

Don't throw an error in case of call spells' callbackSrv with empty args.

Motivation

Aqua now always adds call "callbackSrv" "response" [] even for fire-and-forget scripts, so spell scripts without explicit return calls always try to store empty responses.

Checklist

• The code follows the project's coding conventions and style guidelines.
• All tests related to the changes have passed successfully.
• Documentation has been updated to reflect the changes (if applicable).
• All new and existing unit tests have passed.
• I have self-reviewed my code and ensured its quality.
• I have added/updated necessary comments to aid understanding.

Reviewer Checklist

• Code has been reviewed for quality and adherence to guidelines.
• Tests have been reviewed and are sufficient to validate the changes.
• Documentation has been reviewed and is up to date.
• Any questions or concerns have been addressed.

[linear]

NET-651 Support empty callbackSrv response for spells in nox