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/test-asn1-rlp

@@ -0,0 +1,39 @@
+#! /usr/bin/env bash
+# Compile main + Asn1Rlp equivalence tests and run them.
+# Prefers Homebrew OpenJDK when /usr/bin/java is a macOS stub.
+
+set -euo pipefail
+
+abs_dir="$(cd -P "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+project_dir="$(dirname "$abs_dir")"
+
+if [[ -x /opt/homebrew/opt/openjdk/bin/javac ]]; then
+  export PATH="/opt/homebrew/opt/openjdk/bin:$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
+
+if ! command -v javac >/dev/null || ! javac -version >/dev/null 2>&1; then
+  echo "No working JDK found (javac)." >&2
+  exit 1
+fi
+
+classes="$project_dir/build/classes"
+test_classes="$project_dir/build/test-classes"
+mkdir -p "$classes" "$test_classes"
+
+echo "Using $(javac -version 2>&1)"
+
+# Portable source collection (bash 3.2 has no mapfile)
+main_sources=$(find "$project_dir/src/main/java" -name '*.java' | sort)
+# shellcheck disable=SC2086
+javac --release 21 -d "$classes" $main_sources
+
+test_sources=$(find "$project_dir/src/test/java" -name '*Asn1Rlp*.java' | sort)
+# shellcheck disable=SC2086
+javac --release 21 -cp "$classes" -d "$test_classes" $test_sources
+
+echo "Running Asn1RlpEquivalenceTest..."
+java -cp "$classes:$test_classes" swiss.qpq.gajumaru.core.serialization.Asn1RlpEquivalenceTest