Ensure test mode only runs in the Unity editor

[tudddorrr]

Fixes #186

[claude]

This PR looks good. The single-line fix is correct and well-scoped.

Summary of change: Removing || DEBUG from the #if UNITY_EDITOR || DEBUG guard in CheckTestMode() ensures NUnit detection (and the resulting RequestMock activation) can only occur inside the Unity editor, not in debug builds of a shipped game. The old condition was unnecessary risk — a DEBUG build would not normally contain the NUnit assembly, but the check was still running, leaving open the possibility of accidentally enabling test mode in a non-editor context.

No issues found across any category. Clean fix.