refactor: move helios::core::units to engine namespace

[ThorstenSuckow]

Summary

The C++ namespace helios::core::units should be moved to helios::engine::core::units to be consistent with the engine module hierarchy. The module name (helios.core.units.Unit) is already correct and does not need to change.

Motivation

All engine-level types live under helios::engine::*. The units namespace currently breaks this convention by residing directly under helios::core::units, even though the file physically lives in include/helios/engine/core/units/.

Scope of Change

Namespace rename

include/helios/engine/core/units/Unit.ixx

// Before
export namespace helios::core::units { ... }

// After
export namespace helios::engine::core::units { ... }

Files requiring namespace updates

The following files reference helios::core::units and need updating:

Engine headers (.ixx)

File	Usage
include/helios/engine/runtime/world/Level.ixx	helios::core::units::Unit, helios::core::units::from()
include/helios/engine/modules/spatial/transform/components/ScaleStateComponent.ixx	helios::core::units::Unit (member, params, return type)
include/helios/engine/modules/spatial/transform/systems/ScaleSystem.ixx	helios::core::units::from()
include/helios/engine/builder/gameObject/builders/configs/TransformConfig.ixx	helios::core::units::Unit (default param)

Tests

File	Usage
tests/helios/core/units.test.cpp	using namespace helios::core::units

Examples

File	Usage
examples/scoring_demo/Namespaces.h	using namespace helios::core::units
examples/runtime_test/main.cpp	using namespace helios::core::units
examples/spaceship_shooting/main.cpp	Fully qualified references
examples/spaceship_control/main.cpp	Fully qualified references
examples/enemy_spawn/main.cpp	Fully qualified references
examples/collision_detection/main.cpp	Fully qualified references

Benchmarks

File	Usage
benchmarks/helios/engine/ecs/EntityComponent.benchmark.cpp	import helios.core.units.Unit

Documentation

File	Usage
docs/core-concepts/conventions.md	Code example with import and namespace
docs/heliosapi.md	Code example with import

No changes needed

• Module name helios.core.units.Unit — already correct
• Module partition include/helios/engine/core/units/_module.ixx — export import remains the same
• Files that only use import helios.core.units.Unit without namespace references (e.g., Bounds.ixx, ChaseSystem.ixx, Move2DComponent.ixx, etc.) — these only need the namespace update if they reference the namespace directly

Checklist

• Rename namespace in Unit.ixx to helios::engine::core::units
• Update all .ixx files with qualified namespace references
• Update all test files
• Update all example files
• Update all benchmark files
• Update documentation (conventions.md, heliosapi.md)
• Build passes (Debug + Release)
• All tests pass
• Update CHANGELOG.md under [Unreleased]