Adopt AGP 9 defaults + enable Gradle configuration cache (#62)

- Remove android.enableJetifier=true. 'gradlew checkJetifier' confirms no
  module uses legacy android.support.* libraries, so Jetifier transforms
  nothing. The flag is removed in AGP 10; omitting it adopts the default (false).
- Remove android.nonFinalResIds=false to adopt the AGP 9 default (true).
  No Java 'switch (R.id.x)'/'case R.id.x:' usage exists (all switches are on
  protocol/type/authType ints), so non-final R ids are safe. Flag removed in AGP 10.
- Enable org.gradle.configuration-cache=true. Verified: a clean
  app:assembleOssDebug stores the entry, and a re-run reuses it (47s -> 1s)
  with renameApksForOssDebug still producing the NekoBox-*-<abi>.apk files.

Both deprecation warnings that AGP 9 emitted are now gone.

Author: hawkff

gradle.properties

@@ -15,11 +15,17 @@ org.gradle.jvmargs=-Xmx4g -XX:+UseParallelGC -Dfile.encoding=UTF-8
 # Android operating system, and which are packaged with your app's APK
 # https://developer.android.com/topic/libraries/support-library/androidx-rn
 android.useAndroidX=true
-# Automatically convert third-party libraries to use AndroidX
-android.enableJetifier=true
+# Jetifier (legacy android.support.* -> androidx rewriting) is intentionally NOT enabled.
+# `./gradlew checkJetifier` confirms no module uses legacy support libraries, and the
+# android.enableJetifier flag is removed in AGP 10. Omitting it adopts the AGP 9 default (false).
 # Kotlin code style for this project: "official" or "obsolete":
 kotlin.code.style=official
 # Gradle parallel build
 org.gradle.parallel=true
+# Gradle configuration cache: caches the result of the configuration phase so subsequent
+# builds skip straight to task execution. Stable since Gradle 8.1.
+org.gradle.configuration-cache=true
 android.nonTransitiveRClass=false
-android.nonFinalResIds=false
+# android.nonFinalResIds is left at the AGP 9 default (true). The project has no Java
+# `switch (R.id.x)` / `case R.id.x:` usage that would require final (constant) R fields,
+# so non-final R ids are safe. The flag is removed in AGP 10.