Improve Gas Yaml Serialization (#40070)

* Make yaml gas serialization cleaner

* fix exception

* fix validation code

* rudimentary test & permissive loading

* change it a bit

* Test fixes and adjustments

Content.IntegrationTests/Tests/Atmos/GasArrayTest.cs

@@ -0,0 +1,85 @@
+using System.Linq;
+using Content.Shared.Atmos;
+using Content.Shared.Atmos.Components;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Prototypes;
+
+namespace Content.IntegrationTests.Tests.Atmos;
+
+[TestFixture]
+[TestOf(typeof(Atmospherics))]
+public sealed class GasArrayTest
+{
+    private const string GasTankTestDummyId = "GasTankTestDummy";
+
+    private const string GasTankLegacyTestDummyId = "GasTankLegacyTestDummy";
+
+    [TestPrototypes]
+    private const string Prototypes = $@"
+- type: entity
+  id: {GasTankTestDummyId}
+  components:
+  - type: GasTank
+    air:
+      volume: 5
+      moles:
+        Frezon: 20
+        Oxygen: 10
+
+- type: entity
+  id: {GasTankLegacyTestDummyId}
+  components:
+  - type: GasTank
+    air:
+      volume: 5
+      moles:
+      - 0
+      - 0
+      - 0
+      - 10
+";
+
+    [Test]
+    public async Task TestGasArrayDeserialization()
+    {
+        await using var pair = await PoolManager.GetServerClient();
+        var server = pair.Server;
+
+        var compFactory = server.ResolveDependency<IComponentFactory>();
+        var prototypeManager = server.ResolveDependency<IPrototypeManager>();
+
+        await server.WaitAssertion(() =>
+        {
+            var gasTank = prototypeManager.Index(GasTankTestDummyId);
+            Assert.Multiple(() =>
+            {
+                Assert.That(gasTank.TryGetComponent<GasTankComponent>(out var gasTankComponent, compFactory));
+
+                Assert.That(gasTankComponent!.Air.GetMoles(Gas.Oxygen), Is.EqualTo(10));
+                Assert.That(gasTankComponent!.Air.GetMoles(Gas.Frezon), Is.EqualTo(20));
+                foreach (var gas in Enum.GetValues<Gas>().Where(p => p != Gas.Oxygen && p != Gas.Frezon))
+                {
+                    Assert.That(gasTankComponent!.Air.GetMoles(gas), Is.EqualTo(0));
+                }
+            });
+
+            var legacyGasTank = prototypeManager.Index(GasTankLegacyTestDummyId);
+            Assert.Multiple(() =>
+            {
+                Assert.That(legacyGasTank.TryGetComponent<GasTankComponent>(out var gasTankComponent, compFactory));
+
+                Assert.That(gasTankComponent!.Air.GetMoles(3), Is.EqualTo(10));
+
+                // Iterate through all other gases: check for 0 values
+                for (var i = 0; i < Atmospherics.AdjustedNumberOfGases; i++)
+                {
+                    if (i == 3) // our case with a value.
+                        continue;
+
+                    Assert.That(gasTankComponent!.Air.GetMoles(i), Is.EqualTo(0));
+                }
+            });
+        });
+        await pair.CleanReturnAsync();
+    }
+}