Add ASN.1-to-Java codegen and RLP codec for spend/signed tx subset.

Generate typed records from GajumaruChainObjects.asn, implement Asn1Rlp
and BasicEncoders matching Erlang static serialization, and add golden-vector
equivalence tests against gmser_chain_objects output.

gajumaru-core/bin/compile

@@ -8,14 +8,22 @@ set -e
 abs_dir="$(cd -P $(dirname ${BASH_SOURCE}) && pwd)"
 project_dir="$(dirname $abs_dir)"
 
+# Prefer Homebrew OpenJDK when /usr/bin/java is a macOS stub.
+if [[ -x /opt/homebrew/opt/openjdk/bin/javac ]]; then
+  export PATH="/opt/homebrew/opt/openjdk/bin:$PATH"
+elif [[ -x /opt/homebrew/opt/openjdk@25/bin/javac ]]; then
+  export PATH="/opt/homebrew/opt/openjdk@25/bin:$PATH"
+elif [[ -x /opt/homebrew/opt/openjdk@21/bin/javac ]]; then
+  export PATH="/opt/homebrew/opt/openjdk@21/bin:$PATH"
+fi
+
 # Clean
 rm -rf "$project_dir/build/classes/*"
 rm -f "$project_dir/Testinator.class"
 
 # Build every .java file
 find "$project_dir/src/main/java" -name "*.java" | xargs javac \
-    -source 21 \
-    -target 21 \
+    --release 21 \
     -d "$project_dir/build/classes"
 
 # Build the Testinator thingy