Adds DamageMetabolism and some simple chems (#3958)

* adds damage metabolism

* tweaks words

* metabolism is kinda weird

* adds some simple chemicals

* renames DamageMetabolism to HealthChangeMetabolism

* tweaks like one chemical because it was annoying

* did some changes that the sloth told me to

* adds summary comments for those foolish enough to try and understand my code

* rewrites the component so that is uses a more elegant solution, and handles decimals

* Updates with suggestions from review

* changes stuff idk:

* git cringe

* changes one tiny lil thing

* Apply YAML suggestions

Co-authored-by: DrSmugleaf <DrSmugleaf@users.noreply.github.com>

Co-authored-by: DrSmugleaf <DrSmugleaf@users.noreply.github.com>

Content.Server/Chemistry/Metabolism/HealthChangeMetabolism.cs

@@ -0,0 +1,68 @@
+using Content.Server.GameObjects.Components.Nutrition;
+using Content.Shared.Chemistry;
+using Content.Shared.Interfaces.Chemistry;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization.Manager.Attributes;
+using Content.Shared.Damage;
+using Content.Shared.GameObjects.Components.Damage;
+
+namespace Content.Server.Chemistry.Metabolism
+{
+    /// <summary>
+    /// Default metabolism for medicine reagents. Attempts to find a DamageableComponent on the target,
+    /// and to update its damage values.
+    /// </summary>
+    [DataDefinition]
+    public class HealthChangeMetabolism : IMetabolizable
+    {
+        /// <summary>
+        /// How much of the reagent should be metabolized each sec.
+        /// </summary> 
+        [DataField("rate")]
+        public ReagentUnit MetabolismRate { get; set; } = ReagentUnit.New(1);
+
+        /// <summary>
+        /// How much damage is changed when 1u of the reagent is metabolized.
+        /// </summary>
+        [DataField("healthChange")]
+        public float HealthChange { get; set; } = 1.0f;
+
+        /// <summary>
+        /// Class of damage changed, Brute, Burn, Toxin, Airloss.
+        /// </summary> 
+        [DataField("damageClass")]
+        public DamageClass DamageType { get; set; } =  DamageClass.Brute;
+
+        private float _accumulatedHealth;
+
+        /// <summary>
+        /// Remove reagent at set rate, changes damage if a DamageableComponent can be found.
+        /// </summary>
+        /// <param name="solutionEntity"></param>
+        /// <param name="reagentId"></param>
+        /// <param name="tickTime"></param>
+        /// <returns></returns>
+        ReagentUnit IMetabolizable.Metabolize(IEntity solutionEntity, string reagentId, float tickTime)
+        {
+            if (solutionEntity.TryGetComponent(out IDamageableComponent? health))
+            {
+                health.ChangeDamage(DamageType, (int)HealthChange, true);
+                float decHealthChange = (float) (HealthChange - (int) HealthChange);
+                _accumulatedHealth += decHealthChange;
+
+                if (_accumulatedHealth >= 1)
+                {
+                    health.ChangeDamage(DamageType, 1, true);
+                    _accumulatedHealth -= 1;
+                }
+                
+                else if(_accumulatedHealth <= -1)
+                {
+                    health.ChangeDamage(DamageType, -1, true);
+                    _accumulatedHealth += 1;
+                }
+            }
+            return MetabolismRate;
+        }
+    }
+}