Port miasma from nyano (#8926)

Co-authored-by: Kara <lunarautomaton6@gmail.com>

Content.Server/Atmos/Miasma/PerishableComponent.cs

@@ -0,0 +1,42 @@
+namespace Content.Server.Atmos.Miasma
+{
+    [RegisterComponent]
+    /// <summary>
+    /// This makes mobs eventually start rotting when they die.
+    /// It may be expanded to food at some point, but it's just for mobs right now.
+    /// </summary>
+    public sealed class PerishableComponent : Component
+    {
+        /// <summary>
+        /// Is this progressing?
+        /// </summary>
+        [ViewVariables(VVAccess.ReadWrite)]
+        public bool Progressing = true;
+
+        /// <summary>
+        /// How long this creature has been dead.
+        /// </summary>
+        [DataField("deathAccumulator")]
+        [ViewVariables(VVAccess.ReadWrite)]
+        public float DeathAccumulator = 0f;
+
+        /// <summary>
+        /// When DeathAccumulator is greater than this, start rotting.
+        /// </summary>
+        public TimeSpan RotAfter = TimeSpan.FromMinutes(3);
+
+        /// <summary>
+        /// Gasses are released every second.
+        /// </summary>
+        [DataField("rotAccumulator")]
+        public float RotAccumulator = 0f;
+
+        /// <summary>
+        /// How many moles of gas released per second, adjusted for mass.
+        /// Humans have a mass of 70. I am aiming for ten mols a minute, so
+        /// 1/6 of a minute, divided by 70 as a baseline.
+        /// </summary>
+        [ViewVariables(VVAccess.ReadWrite)]
+        public float MolsPerSecondPerUnitMass = 0.0025f;
+    }
+}