Add Trapezoidal suitability function and corresponding tests

Introduced a new Trapezoid method in the Suitability class to model suitability with a hard tolerance band and a plateau. The method returns suitability values based on defined limits and optimal ranges. Added comprehensive unit tests to validate the functionality, including edge cases for flat plateaus, linear ramps, and hard limits.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/MrGameEng.Simulation.Tests/AI/SuitabilityTests.cs

@@ -48,4 +48,45 @@ public class SuitabilityTests
         Assert.Equal(1f, Suitability.Gaussian(5f, 5f, 0f));
         Assert.Equal(0f, Suitability.Gaussian(6f, 5f, 0f));
     }
+
+    [Fact]
+    public void Trapezoid_IsFlatAcrossThePlateau()
+    {
+        Assert.Equal(1f, Suitability.Trapezoid(10f, 0f, 10f, 42f, 58f), 5);
+        Assert.Equal(1f, Suitability.Trapezoid(25f, 0f, 10f, 42f, 58f), 5);
+        Assert.Equal(1f, Suitability.Trapezoid(42f, 0f, 10f, 42f, 58f), 5);
+    }
+
+    [Fact]
+    public void Trapezoid_RampsLinearlyOnEachShoulder()
+    {
+        Assert.Equal(0.5f, Suitability.Trapezoid(5f, 0f, 10f, 42f, 58f), 5); // halfway up the cold ramp
+        Assert.Equal(0.5f, Suitability.Trapezoid(50f, 0f, 10f, 42f, 58f), 5); // halfway down the heat ramp
+    }
+
+    [Fact]
+    public void Trapezoid_IsZeroAtAndBeyondTheHardLimits()
+    {
+        Assert.Equal(0f, Suitability.Trapezoid(0f, 0f, 10f, 42f, 58f));
+        Assert.Equal(0f, Suitability.Trapezoid(-5f, 0f, 10f, 42f, 58f));
+        Assert.Equal(0f, Suitability.Trapezoid(58f, 0f, 10f, 42f, 58f));
+        Assert.Equal(0f, Suitability.Trapezoid(70f, 0f, 10f, 42f, 58f));
+    }
+
+    [Fact]
+    public void Trapezoid_DegenerateShoulder_IsAHardStep()
+    {
+        // optimalLow == min: full suitability immediately above the lower limit, zero at/below it.
+        Assert.Equal(1f, Suitability.Trapezoid(5f, 0f, 0f, 10f, 20f));
+        Assert.Equal(0f, Suitability.Trapezoid(0f, 0f, 0f, 10f, 20f));
+    }
+
+    [Fact]
+    public void Trapezoid_StaysWithinUnitRange()
+    {
+        for (var v = -50f; v <= 80f; v += 1f)
+        {
+            Assert.InRange(Suitability.Trapezoid(v, 0f, 10f, 42f, 58f), 0f, 1f);
+        }
+    }
 }