Support libsignal 0.101.0 Android JNI classifiers

[dvrdnz]

Summary

Update signal-cli to libsignal-client 0.101.0 and add support for consuming the Android JNI classifier artifacts published by the corresponding libsignal change (libsignal/pull/689).

Changes

• Stop relying on the transitive libsignal-client dependency from signal-network.
• Depend explicitly on org.signal:libsignal-client:0.101.0.
• Add an optional androidClassifier Gradle property for platform-specific JNI artifacts.
• Keep the existing libsignal_client_path local-JAR override.
• Migrate SessionStore to the libsignal-client 0.101.0 hasSenderChain() API.

Android classifier

For example:

-PandroidClassifier=android-aarch64

resolves:

org.signal:libsignal-client:0.101.0
+
org.signal:libsignal-client:0.101.0:android-aarch64

The normal JAR provides the Java API while the classifier provides libsignal_jni.so.

Validation

Verified on Termux / Android aarch64:

./gradlew clean classes
./gradlew :libsignal-cli:compileTestJava
./gradlew --offline \
  -PandroidClassifier=android-aarch64 \
  :libsignal-cli:clean \
  :libsignal-cli:test

The Android-classifier test completed successfully.

This PR depends on the corresponding libsignal change that publishes the Android JNI classifier artifacts.