Persisted Forge build caches

- Sandboxed Forge lanes retain Mavenizer and ForgeGradle caches in their private Gradle home
- Nested mod builds receive the sandbox property

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'