Replace benchmark.cc with a Python script

Background

bin/benchmark.cc directly uses google::protobuf::Arena to allocate QueryResponse messages. Because libneug.so hides all protobuf symbols via the version script (cmake/neug_exports.ld), the benchmark binary cannot link ${Protobuf_LIBRARIES} without causing duplicate libprotobuf runtime issues (#387).

PR #491 removed the explicit protobuf linkage from all other consumer targets, but benchmark.cc still has direct Arena usage that needs to be addressed.

Proposal

Replace bin/benchmark.cc with a Python script that uses neug_py_bind to run benchmarks. This:

• Eliminates the last direct protobuf dependency in consumer binaries
• Simplifies the build matrix (benchmark target can be removed from bin/CMakeLists.txt)
• Makes benchmarks easier to extend and parameterize without recompilation
• Leverages the existing Python binding infrastructure

Scope

• Port benchmark.cc functionality to a Python script (config parsing, query execution loop, timing)
• Remove benchmark.cc and its CMake target from bin/CMakeLists.txt
• Verify equivalent performance measurement accuracy through Python bindings

Related

• #387 — duplicate libprotobuf runtime bug
• #490 — remove explicit ${Protobuf_LIBRARIES} linkage
• #491 — PR removing protobuf linkage from other targets