Hydrology pool host cap

- Hydrology planner pool minimum never exceeds the host core count (floor 2)

core/src/main/java/art/arcane/iris/generation/concurrent/MultiBurst.java

@@ -144,11 +144,11 @@ public class MultiBurst extends MultiBurstSupport {
         }
 
         static int plannerParallelism() {
-            return plannerParallelism(MultiBurstSupport.performanceProcessors());
+            return plannerParallelism(MultiBurstSupport.performanceProcessors(), Runtime.getRuntime().availableProcessors());
         }
 
-        static int plannerParallelism(int performanceProcessors) {
+        static int plannerParallelism(int performanceProcessors, int availableProcessors) {
-            return Math.max(4, performanceProcessors);
+            return Math.max(2, Math.min(Math.max(4, performanceProcessors), availableProcessors));
         }
 
         @Override

core/src/test/java/art/arcane/iris/generation/concurrent/HydrologyBurstTest.java

@@ -63,9 +63,17 @@ public class HydrologyBurstTest {
 
     @Test
     public void plannerPoolFollowsThePerformanceCores() {
-        assertEquals(12, MultiBurst.HydrologyBurst.plannerParallelism(12));
+        assertEquals(12, MultiBurst.HydrologyBurst.plannerParallelism(12, 16));
-        assertEquals(4, MultiBurst.HydrologyBurst.plannerParallelism(1));
+        assertEquals(4, MultiBurst.HydrologyBurst.plannerParallelism(1, 8));
-        assertEquals(32, MultiBurst.HydrologyBurst.plannerParallelism(32));
+        assertEquals(32, MultiBurst.HydrologyBurst.plannerParallelism(32, 32));
+    }
+
+    @Test
+    public void plannerPoolNeverOutgrowsASmallHost() {
+        assertEquals(2, MultiBurst.HydrologyBurst.plannerParallelism(1, 1));
+        assertEquals(2, MultiBurst.HydrologyBurst.plannerParallelism(2, 2));
+        assertEquals(3, MultiBurst.HydrologyBurst.plannerParallelism(3, 3));
+        assertEquals(4, MultiBurst.HydrologyBurst.plannerParallelism(2, 4));
     }
 
     @Test