chore: update Android Gradle build to support the newer Flutter SDK

- Upgraded Gradle to 8.12.1
- Changed compile and target compatibility to Java 17 with corresponding Kotlin JVM target
- Set `compileSdkVersion` to use Flutter's value.
- Added compiler flags for unchecked and deprecation warnings.

Author: ttypic

android/build.gradle

@@ -1,14 +1,18 @@
 group 'io.ably.flutter.plugin'
-version '1.0'
+// Use the snapshot suffix to show that build artifacts are not shared.
+// This Gradle file is used by Flutter to build itself.
+version '1.0-SNAPSHOT'
 
 buildscript {
+    ext.kotlin_version = '2.2.10'
     repositories {
         google()
-        mavenCentral() // for firebase-messaging
+        mavenCentral()
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:7.4.0'
+        classpath 'com.android.tools.build:gradle:8.12.1'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
     }
 }
 
@@ -33,22 +37,25 @@ dependencies {
 }
 
 android {
-    compileSdkVersion 34
+    compileSdkVersion flutter.compileSdkVersion
 
     // Conditional for compatibility with AGP <4.2.
     if (project.android.hasProperty("namespace")) {
         namespace 'io.ably.flutter.plugin'
     }
 
-    // Require Java language level 8 so we can use Method References (used with Lambdas)
     compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_8
-        targetCompatibility JavaVersion.VERSION_1_8
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
 
         // Flag to enable Java 8 language APIs while supporting to older SDK Versions
         coreLibraryDesugaringEnabled true
     }
 
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17.toString()
+    }
+
     defaultConfig {
         minSdkVersion 19
 
@@ -66,4 +73,10 @@ android {
     }
 }
 
+gradle.projectsEvaluated {
+    tasks.withType(JavaCompile) {
+        options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
+    }
+}
+
 apply from: file("./ably-agent.gradle")