feat(core): add criterion bench_*.rs / *_bench.rs to Rust group

Most Rust benchmarks live under `benches/` (already covered by the
directory rule added earlier in this branch), so these file-name
patterns are mostly a defensive belt-and-braces for the small set of
Cargo workspaces that keep bench targets alongside library code
rather than under the canonical `benches/` tree.

Kept commented-out; contributes negligibly to the token savings for
mainstream layouts but preserves symmetry with the C++ group, which
already ships `*_benchmark.cc` and `*Benchmark.cpp`.