add type assertion to logger

[garmr-ulfr]

Just adds type assertion

[Copilot]

Pull Request Overview

This PR refactors the logger initialization in NewMutableURLTest to safely handle type assertions, replacing a direct type assertion with a type-safe check.

• Replaces unsafe type assertion with safe type checking using the comma ok idiom
• Conditionally creates a specialized logger factory only when the logger implements the sbxL.SLogger interface
• Falls back to using the original logger when type assertion fails

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