Fixing fallbacks for macos Folk

Compiles fine, just stricter defaults

buildSrc/build.gradle.kts

@@ -1,7 +1,23 @@
+import org.gradle.jvm.toolchain.JavaLanguageVersion
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+
 plugins {
     kotlin("jvm") version embeddedKotlinVersion
 }
 
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(21))
+    }
+}
+
+kotlin {
+    jvmToolchain(21)
+    compilerOptions {
+        jvmTarget.set(JvmTarget.JVM_21)
+    }
+}
+
 repositories {
     mavenCentral()
     gradlePluginPortal()
@@ -13,4 +29,4 @@ dependencies {
     implementation("com.github.VolmitSoftware:NMSTools:c88961416f")
     implementation("io.papermc.paperweight:paperweight-userdev:2.0.0-beta.18")
     implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.10.2")
-}
+}