Revert to PyO3 0.20 and limit Python to 3.9-3.12

PyO3 0.21+ has breaking API changes and ndarray ecosystem
compatibility issues. Reverting to working 0.20 versions:
- PyO3 0.20 (supports Python 3.7-3.12)
- numpy 0.20 (compatible with ndarray 0.15)

Python 3.13+ support will be added when ecosystem catches up.

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

Author: igerber

.github/workflows/publish.yml

@@ -20,7 +20,7 @@ jobs:
         uses: PyO3/maturin-action@v1
         with:
           target: ${{ matrix.target }}
-          args: --release --out dist -i python3.9 -i python3.10 -i python3.11 -i python3.12 -i python3.13
+          args: --release --out dist -i python3.9 -i python3.10 -i python3.11 -i python3.12
           manylinux: auto
           # Install OpenBLAS in manylinux container
           before-script-linux: |
@@ -38,7 +38,7 @@ jobs:
     runs-on: macos-13  # x86_64 runner
     strategy:
       matrix:
-        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
+        python-version: ['3.9', '3.10', '3.11', '3.12']
     steps:
       - uses: actions/checkout@v4
 
@@ -73,7 +73,7 @@ jobs:
     runs-on: macos-latest  # ARM64 runner
     strategy:
       matrix:
-        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
+        python-version: ['3.9', '3.10', '3.11', '3.12']
     steps:
       - uses: actions/checkout@v4
 
@@ -108,7 +108,7 @@ jobs:
     runs-on: windows-latest
     strategy:
       matrix:
-        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
+        python-version: ['3.9', '3.10', '3.11', '3.12']
     steps:
       - uses: actions/checkout@v4
 

rust/Cargo.toml

@@ -16,8 +16,11 @@ default = []
 extension-module = ["pyo3/extension-module"]
 
 [dependencies]
-pyo3 = "0.22"
-numpy = "0.22"
+# PyO3 0.20 supports Python 3.7-3.12
+# numpy 0.20 is compatible with ndarray 0.15 (same as ndarray-linalg)
+# Python 3.13+ support pending ecosystem updates
+pyo3 = "0.20"
+numpy = "0.20"
 ndarray = { version = "0.15", features = ["rayon"] }
 rand = "0.8"
 rand_xoshiro = "0.6"