Fix Ghidra xref attachments

[DarkaMaul]

Summary

• attach Ghidra address references to block-level instruction xref fields
• populate data xref fields from the exported reference table
• add a Ghidra integration regression test for Python xref APIs

Verification

• env JAVA_HOME=/Users/dm/Library/Java/JavaVirtualMachines/temurin-21.0.1/Contents/Home GHIDRA_INSTALL_DIR=/opt/homebrew/opt/ghidra/libexec GRADLE_USER_HOME=/Users/dm/Projects/Exporters/quokka.dm-ghidra-xref/.gradle ./gradlew buildExtension
• env JAVA_HOME=/Users/dm/Library/Java/JavaVirtualMachines/temurin-21.0.1/Contents/Home GHIDRA_INSTALL_DIR=/opt/homebrew/opt/ghidra/libexec XDG_CONFIG_HOME=/Users/dm/Projects/Exporters/quokka.dm-ghidra-xref/.ghidra-runtime .venv/bin/python -m pytest tests/python/tests/ghidra/test_ghidra_export.py::TestPuraUpdateGhidraExport::test_xrefs_attached_to_python_objects -q
• manual quokka-cli Ghidra export of docs/samples/qb-crackme, then Python API xref checks: block xrefs 293/203, data xrefs 28/130, functions with callees/callers 31/24