Refactor Unity test scripts: culture-invariant parsing, parenting, and safety improvements

[cassiussa]

Motivation

• Improve reliability and modernize several editor/runtime test scripts by making numeric parsing culture-invariant and consolidating file I/O.
• Reduce accidental component duplication and improve transform parenting semantics in scene construction code.
• Harden utility types by making pure helper classes static and implementing equality/hash semantics for value types.

Description

• Renamed and made the editor helper class static (Tags -> MakeLayers) and adjusted constructor/method visibility to static/private in MakeLayers.cs.
• Replaced direct string double.Parse calls with a culture-invariant helper ParseDouble(JSONNode) in CreateSolarSystems.cs and updated parsing in Elements (RightAscension and Declination) to use CultureInfo.InvariantCulture.
• Centralized JSON loading in ImportData.Data by computing FileName via Application.dataPath and adding LoadJson() which returns File.ReadAllText(FileName).
• Replaced deprecated/less-robust parenting via transform.parent = ... with transform.SetParent(..., true) and added [DisallowMultipleComponent] to several MonoBehaviours (CreateCameras, CreateSolarSystems, SystemScaleState).
• Made Maths a static class and removed unused usings across several files to reduce clutter.
• Added Equals and GetHashCode implementations for Vector3d and provided an implicit cast to Vector3, and made minor API accessibility adjustments like SerializeField for camDepth and use of cam.cullingMask.
• Other whitespace/usings cleanup and small fixes across CreateCameras.cs, CreateElements.cs, SystemScaleState.cs, and several test scripts.

Testing

• No automated tests were executed as part of this change set.

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Codex Task