v0.56.1

- Further updates to the backup validator

- Simplify the Android build to not have a separate "testing-fns"
  variant of the Rust library, fixing incremental builds

- Removed the libWithDebugSymbols Maven artifact for libsignal-android
  now that the libraries are packaged unstripped

- Updated Gradle, Android Gradle Plugin, and Android NDK versions

- Internal work in SVR and libsignal-net