Fix benchmark workflow configuration

## Summary - Replace the pair of benchmark workflow files with the single correct `benchmark.yml` - Use AirspeedVelocity.jl action v1 for consolidated benchmarking - Properly handle both pull requests and main branch benchmarking ## Changes - Removed: `benchmark.yml` and `benchmark-comment.yml` (old split configuration) - Added: Single `benchmark.yml` using `MilesCranmer/AirspeedVelocity.jl@action-v1` ## Benefits - Simpler workflow configuration - Consistent with other packages in the ecosystem (e.g., PBCCompiler.jl) - Uses the latest AirspeedVelocity.jl action 🤖 Generated with [Claude Code](https://claude.com/claude-code)