Refactor save manager validation and update state structure

- Updated the save manager to enforce a new format version (2) and improved validation checks for the save data structure.
- Enhanced the `validate_data` function to ensure all required fields are present and valid.
- Adjusted the handling of legacy saves and introduced new checks for various state fields.
- Improved number formatting in the global script for better readability of large numbers.
- Updated tests to reflect changes in the save manager and validation logic, ensuring compatibility with the new state structure.
- Added new tests for group indexing and production transactions to ensure correctness of entity management and resource production.

tests/test_production_transaction.gd

@@ -0,0 +1,58 @@
+extends SceneTree
+const Clock = preload("res://world/owniverse/simulation_time.gd")
+var checks: int = 0
+var failures: int = 0
+
+func _initialize() -> void:
+    call_deferred("run")
+
+func check(condition: bool, message: String) -> void:
+    checks += 1
+    if not condition:
+        failures += 1
+        push_error(message)
+
+func fixture():
+    var world = load("res://world/owniverse/owniverse.gd").new()
+    var global: Node = root.get_node("Global")
+    for id in global.OwniverseEntities:
+        var entity = load("res://world/owniverse/owniverse_entity.gd").new(global.OwniverseEntities[id])
+        world.entities[id] = entity
+        world.state.amount[id] = 0.0
+        world.state.stats.total_amount[id] = 0.0
+        if entity.group_as != "":
+            world.state.amount[entity.group_as] = 0.0
+            world.state.stats.total_amount[entity.group_as] = 0.0
+    world.entities["N"].life_product = {}
+    world.entities["N"].product_per_year_type = "H"
+    world.entities["N"].product_per_year_amount = 10.0
+    world.entities["N"].auto = 0.0
+    world.state.amount.N = 1.0
+    return world
+
+func dispose(world) -> void:
+    for entity in world.entities.values():
+        entity.free()
+    world.free()
+
+func run() -> void:
+    var world = fixture()
+    world.initialize_life_batches()
+    world.entities.N.cost = {"H": 2.0}
+    world.entities.N.bind = {"S": 3.0}
+    world.state.amount.H = 10.0
+    world.state.amount.S = 0.0
+    world.state.auto_resources = {"H": 10.0}
+    world.state.batches.H = [{"amount": 10.0, "start_year": 1.0, "end_year": 2.0}]
+    var before: Dictionary = world.state.duplicate(true)
+    check(not world._try_production(world.state, world.entities.N, 1.0, true), "Binding failure rejects production")
+    check(world.state == before, "Failure preserves costs, batches and budget")
+    world.state.amount.S = 10.0
+    var old_batches: Array = world.state.batches.H
+    check(world._try_production(world.state, world.entities.N, 2.0, true), "Funded production succeeds")
+    check(world.state.amount.H == 6.0 and world.state.amount.S == 4.0, "Exact cost and binding")
+    check(world.state.auto_resources.H == 6.0, "Exact automatic budget")
+    check(old_batches[0].amount == 10.0 and world.state.batches.H[0].amount == 6.0, "Consumed batches isolated")
+    print("Transaction: %d checks, %d failures" % [checks, failures])
+    dispose(world)
+    quit(1 if failures else 0)