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_async_save.gd

@@ -22,6 +22,7 @@ func run() -> void:
     manager.save_completed.connect(func(filename, success, error): completions.append([filename, success, error]))
     var world = load("res://world/owniverse/owniverse.gd").new()
     var data: Dictionary = {"state": world.state, "ui": {"current_page": 1}}
+    var initial_energy: float = world.state.energy
     var global: Node = root.get_node("Global")
     var old_plaintext: bool = global.save_plaintext_copy
     global.save_plaintext_copy = true
@@ -35,9 +36,9 @@ func run() -> void:
         await process_frame
     check(not manager.is_saving() and frames > 0, "Frames continue while save is pending")
     var saved: Dictionary = manager.load_data("snapshot", "test-password")
-    check(saved.state.energy == 1e14 and saved.ui.current_page == 1, "Worker owns a deep snapshot")
+    check(saved.state.energy == initial_energy and saved.ui.current_page == 1, "Worker owns a deep snapshot")
     var plain: Dictionary = JSON.parse_string(FileAccess.get_file_as_string(directory.path_join("snapshot.adventure.json")))
-    check(plain.state.energy == 1e14, "Diagnostic JSON uses same snapshot")
+    check(plain.state.energy == initial_energy, "Diagnostic JSON uses same snapshot")
     check(completions.size() == 1 and completions[0][1], "Completion reports successful write")
 
     completions.clear()