Add nitrous oxide synthesis reaction (#22774)

Co-authored-by: whateverusername0 <whateveremail>
Co-authored-by: Kevin Zheng <kevinz5000@gmail.com>

Content.Server/Atmos/Reactions/MiasmaOxygenReaction.cs

@@ -0,0 +1,33 @@
+using Content.Server.Atmos.EntitySystems;
+using Content.Shared.Atmos;
+using JetBrains.Annotations;
+
+namespace Content.Server.Atmos.Reactions;
+
+[UsedImplicitly]
+public sealed partial class MiasmaOxygenReaction : IGasReactionEffect
+{
+    public ReactionResult React(GasMixture mixture, IGasMixtureHolder? holder, AtmosphereSystem atmosphereSystem, float heatScale)
+    {
+        var nMiasma = mixture.GetMoles(Gas.Miasma);
+        var nOxygen = mixture.GetMoles(Gas.Oxygen);
+        var nTotal = mixture.TotalMoles;
+
+        // Concentration-dependent reaction rate
+        var fMiasma = nMiasma/nTotal;
+        var fOxygen = nOxygen/nTotal;
+        var rate = MathF.Pow(fMiasma, 2) * MathF.Pow(fOxygen, 2);
+
+        var deltaMoles = nMiasma / Atmospherics.MiasmaOxygenReactionRate * 2 * rate;
+
+        if (deltaMoles <= 0 || nMiasma - deltaMoles < 0)
+            return ReactionResult.NoReaction;
+
+        mixture.AdjustMoles(Gas.Miasma, -deltaMoles);
+        mixture.AdjustMoles(Gas.Oxygen, -deltaMoles);
+        mixture.AdjustMoles(Gas.NitrousOxide, deltaMoles / 2);
+        mixture.AdjustMoles(Gas.WaterVapor, deltaMoles * 1.5f);
+
+        return ReactionResult.Reacting;
+    }
+}