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.

autoload/global.gd

@@ -66,15 +66,15 @@ func format_number(value: float, digits: int = 0) -> String:
         var fixed: String = "%.*f" % [digits, value]
         var parts: PackedStringArray = fixed.split(".", true)
         var integer: String = parts[0]
-        var sign: String = ""
+        var sign_prefix: String = ""
         if integer.begins_with("-") or integer.begins_with("+"):
-            sign = integer.left(1)
+            sign_prefix = integer.left(1)
             integer = integer.substr(1)
         var grouped: String = ""
         while integer.length() > 3:
             grouped = " " + integer.right(3) + grouped
             integer = integer.left(integer.length() - 3)
-        grouped = sign + integer + grouped
+        grouped = sign_prefix + integer + grouped
         return grouped + ("." + parts[1] if parts.size() > 1 else "")
 
     var exp_value = int(floor(log(abs(value)) / log(10.0)))