Improved isolated Iris builds

- Bukkit builds allocate four workers and 8 GiB for tests
- Forge sandbox builds retain their private Minecraft dependency cache

adapters/forge/build.gradle

@@ -66,10 +66,13 @@ String forgeVersion = providers.gradleProperty('forgeVersion').getOrElse(irisMod
 String buildLane = gradle.extensions.extraProperties.has('irisBuildLane')
     ? gradle.extensions.extraProperties.get('irisBuildLane').toString() : null
 if (buildLane != null) {
+    File laneCache = providers.gradleProperty('multiplexorSandbox').getOrElse('false').toBoolean()
+        ? new File(gradle.gradleUserHomeDir, "caches/iris-forge/${buildLane}")
+        : file(".gradle/iris-lanes/${buildLane}")
     plugins.withType(EnhancedPlugin).configureEach { EnhancedPlugin<?> forgePlugin ->
-        forgePlugin.globalCaches().set(layout.projectDirectory.dir(".gradle/iris-lanes/${buildLane}/forgegradle"))
+        forgePlugin.globalCaches().set(new File(laneCache, 'forgegradle'))
     }
-    minecraft.mavenizerOutput.set(layout.projectDirectory.dir(".gradle/iris-lanes/${buildLane}/mavenizer/repo"))
+    minecraft.mavenizerOutput.set(new File(laneCache, 'mavenizer/repo'))
 }
 Closure<String> loaderDisplayVersion = { String loaderVersion ->
     String coordinatePrefix = "${minecraftVersion}-"

build.gradle

@@ -334,7 +334,7 @@ Provider<IrisModdedBuildService> matrixWorkers = gradle.sharedServices.registerI
 }
 List<String> nestedBuildArguments = [gradle.startParameter.buildCacheEnabled ? '--build-cache' : '--no-build-cache']
 if (providers.gradleProperty('multiplexorSandbox').getOrElse('false').toBoolean()) {
-    nestedBuildArguments.add('--no-daemon')
+    nestedBuildArguments.addAll(['--no-daemon', '-PmultiplexorSandbox=true'])
 }
 String nestedJvmArguments = providers.gradleProperty('org.gradle.jvmargs').getOrElse('') +
     ' -XX:ActiveProcessorCount=2'

gradle/multiplexor.gradle

@@ -40,7 +40,7 @@ gradle.projectsEvaluated {
     File spiArtifact = project(':spi').tasks.named('jar', Jar).get().archiveFile.locationOnly.get().asFile
     buildTargets.addAll([
         [id: 'bukkit', tasks: [':buildBukkit'], arguments: [], java: 25,
-            memoryMiB: 6144, workers: 2, dependsOn: [], artifacts: [
+            memoryMiB: 8192, workers: 4, dependsOn: [], artifacts: [
                 [path: relativePath(bukkitArtifact), role: 'runtime', platforms: ['plugin'], minecraftVersions: bukkitVersions]]],
         [id: 'api', tasks: [':irisApi'], arguments: [], java: 25,
             memoryMiB: 6144, workers: 2, dependsOn: [], artifacts: [