Add C11 vs Fortran77 benchmark infrastructure

- Native C benchmarks for BB01AD, BB02AD, BB03AD, BB04AD, BD01AD, BD02AD, SB02MD, SB02OD, SB03MD, SB03OD
- Python script for C vs Fortran comparison with markdown report
- pytest-benchmark added to test dependencies
- README with prerequisites and usage

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jamestjsp

benchmarks/README.md

@@ -0,0 +1,78 @@
+# SLICOT Benchmarks
+
+Two benchmark suites: **Python wrapper benchmarks** (pytest-benchmark) and **C vs Fortran benchmarks** (native).
+
+## Python Wrapper Benchmarks
+
+pytest-benchmark tests for the Python API.
+
+```bash
+# Install pytest-benchmark
+pip install pytest-benchmark
+
+# Run benchmarks
+pytest benchmarks/ --benchmark-only
+```
+
+## C11 vs Fortran77 Benchmarks
+
+Compares native C11 implementation against original Fortran77.
+
+### Prerequisites
+
+1. **Build C library with benchmarks**
+   ```bash
+   meson setup build && meson compile -C build
+   ```
+
+2. **Build Fortran reference library**
+   ```bash
+   cd SLICOT-Reference
+   cmake -B build_bench
+   cmake --build build_bench
+   cd ..
+   ```
+
+### Running
+
+```bash
+# Full comparison (generates markdown report)
+python scripts/benchmark_c_vs_fortran.py --output benchmark_report.md
+
+# Custom build directory
+python scripts/benchmark_c_vs_fortran.py --c-build-dir build --output report.md
+
+# Specific routines only
+python scripts/benchmark_c_vs_fortran.py -r bb01ad sb02md
+
+# Run native C benchmarks via meson
+meson benchmark -C build
+```
+
+### Output
+
+Generates `benchmark_report.md` with:
+- Executive summary (speedup statistics)
+- System configuration
+- Per-routine comparison tables
+- Raw benchmark data (CSV)
+
+### Routines Benchmarked
+
+| Routine | Description |
+|---------|-------------|
+| BB01AD | CAREX - Continuous-time Riccati examples |
+| BB02AD | DAREX - Discrete-time Riccati examples |
+| BB03AD | CTLEX - Continuous-time Lyapunov examples |
+| BB04AD | DTLEX - Discrete-time Lyapunov examples |
+| BD01AD | CTDSX - Continuous-time descriptor examples |
+| BD02AD | DTDSX - Discrete-time descriptor examples |
+| SB03MD | Continuous-time Lyapunov solver |
+| SB03OD | Discrete-time Lyapunov solver (Cholesky) |
+
+### Requirements
+
+- Python 3.8+
+- gfortran (for Fortran benchmarks)
+- meson, ninja (for C build)
+- BLAS/LAPACK (Accelerate on macOS, OpenBLAS on Linux)