Refactor Owniverse modules for quantity mathematics and entity catalog

- Introduced `quantity_math.gd` for arithmetic operations including allocation, normalization, and accumulation of quantities without scene tree dependencies.
- Created `entity_catalog.gd` to manage entity definitions, groups, and event indexes, ensuring separation from simulation state and UI.
- Implemented `item_presentation.gd` for read-only projections of simulation state, handling amounts and unlock conditions for UI elements.
- Updated `civilization_evolution.gd` and `civilization_state.gd` to utilize new quantity math functions, improving code clarity and maintainability.
- Enhanced tests in `test_quantity_catalog.gd` to validate new functionality and ensure correctness of mathematical operations.
- Revised documentation to reflect changes in module structure and functionality.

tests/test_time.gd

@@ -70,7 +70,8 @@ func run() -> void:
     world.evolute(0.005)
     check(world.state.time.year == 0.1, "Speed change preserves accumulated fraction")
     world.speed = 100
-    check(world.speed == 5 and world.state.speed_in_year == 10000.0, "Upper speed limit unchanged")
+    var speed_limit: int = root.get_node("Global").SPEED_LIMIT
+    check(world.speed == speed_limit and world.state.speed_in_year == pow(10.0, speed_limit - 1), "Configured upper speed limit")
     world.speed = -10
     check(world.speed == 1 and world.state.speed_in_year == 1.0, "Lower speed limit unchanged")
     dispose(world)