Add commands to run PGO optimization

PGO.md

@@ -0,0 +1,11 @@
+# PGO
+
+- Requires maturin >= 1.13 and `rustup component add llvm-tools` (for llvm-profdata).
+- `maturin develop` ignores PGO — build the wheel explicitly:
+
+  `maturin build --release --pgo`
+
+- This runs a 3-phase build. 1) instrumented wheel 2) trains by running `pgo-command` from pyproject.toml (`python src/bench_parse_games.py`) in a temp venv 3) optimized rebuild.
+- Training needs `2013-07-train-00000-of-00001.parquet` in the working dir.
+- Optimized wheel lands in `target/wheels/`; install with `pip install --force-reinstall --no-deps target\wheels\rust_pgn_reader_python_binding-*-win_amd64.whl`.
+- Measured vs main (median of 5 interleaved runs): MT parse 0.176s → 0.146s (~17% faster), ST parse 1.34s → 1.23s (~8% faster).

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["maturin>=1.7,<2.0"]
+requires = ["maturin>=1.13,<2.0"]
 build-backend = "maturin"
 
 [project]
@@ -17,3 +17,4 @@ dependencies = [
 ]
 [tool.maturin]
 features = ["pyo3/extension-module"]
+pgo-command = "python src/bench_parse_games.py"