Gradle's buildRustCertgen task requires cargo-ndk and Android NDK
targets to cross-compile libcertgen.so. Without these, CI fails on
any commit after 6aba82e which wired the Rust crate into the pipeline.
The CI build was failing with a "JVM garbage collector is thrashing" error due to insufficient memory. This commit increases the Gradle max heap size to 2GB in the GitHub Actions workflow to resolve the build failure.