clean up build.gradle files, move constants to buildSrc

buildSrc/build.gradle.kts

@@ -0,0 +1,11 @@
+plugins {
+    `kotlin-dsl`
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation("net.lingala.zip4j:zip4j:2.9.0")
+}