ci: add automatic performance benchmark CI for pull requests

[Copilot]

Adds automated performance regression detection for pull requests. Benchmarks run on both PR and base branches, with results posted as a comparison comment.

Implementation

• Workflow: .github/workflows/benchmark.yml triggers on PRs to master
• Execution: Runs all tests/benchmarks/ tests via pytest-benchmark on both branches
• Comparison: JavaScript analysis calculates percentage changes, flags regressions >10%
• Output: Posts formatted table with visual indicators (🚀 faster, ⚠️ slower, ✅ similar, 🆕 new)

Comment Format

## 📊 Performance Benchmark Results

### ⚠️ Significant Performance Changes Detected
- test_benchmark_rbac_model: 15.23% slower

### Detailed Comparison
| Benchmark | Status | PR Mean (s) | Base Mean (s) | Change |
|-----------|--------|-------------|---------------|--------|
| test_benchmark_raw | ✅ | 3.0000e-7 | 3.0000e-7 | 0.00% |
| test_benchmark_rbac_model | ⚠️ SLOWER | 5.7615e-6 | 5.0000e-6 | 15.23% |

Leverages existing pytest-benchmark infrastructure, no new dependencies.

Original prompt

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This section details on the original issue you should resolve

<issue_title>ci: add automatic performance benchmark CI for Pull Requests</issue_title>
<issue_description>An automatic CI workflow for performance benchmarking is proposed:

• Benchmark tests are executed automatically when a new Pull Request is submitted.

• Post a clear comparison table in PR comments to show speed differences.

• Help maintainers catch performance regressions before merging.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ci: add automatic performance benchmark CI for Pull Requests #417

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