Trimmed unused build work

- Limited SlimJar generation to shaded core artifacts
- Honored configured mod test fork limits
- Set Forge targets to four test JVMs

gradle/modded-version-sources.gradle

@@ -8,8 +8,8 @@ tasks.named('compileTestJava', JavaCompile).configure {
     options.release.set((int) irisModTarget.java)
 }
 tasks.withType(Test).configureEach {
-    maxParallelForks = Math.min(2, Math.min(Runtime.runtime.availableProcessors(),
-        Math.min(gradle.startParameter.maxWorkerCount, testForks)))
+    maxParallelForks = Math.min(Runtime.runtime.availableProcessors(),
+        Math.min(gradle.startParameter.maxWorkerCount, testForks))
     if (gradle.extensions.extraProperties.has('irisBuildLane')) {
         jvmArgs('-XX:ParallelGCThreads=2', '-XX:ConcGCThreads=1', '-XX:CICompilerCount=2')
     }

gradle/multiplexor.gradle

@@ -60,7 +60,7 @@ gradle.projectsEvaluated {
             buildTargets.add([
                 id: "${loader}-${minecraft}".toString(),
                 tasks: [":verify${label}${minecraft.replace('.', '_')}".toString()],
-                arguments: ['-PmoddedBuildParallelism=1', "-PmoddedTestForks=${forge ? 2 : 1}".toString(),
+                arguments: ['-PmoddedBuildParallelism=1', "-PmoddedTestForks=${forge ? 4 : 1}".toString(),
                     '-PmultiplexorSandbox=true'],
                 java: 25,
                 memoryMiB: forge ? 16384 : 8192,