fix(ci): pyo3 ABI3 forward-compat for python 3.14

Author: nikolay-e

.github/workflows/ci.yml

@@ -161,6 +161,8 @@ jobs:
 
       - name: Build and install diffctx Rust extension
         shell: bash
+        env:
+          PYO3_USE_ABI3_FORWARD_COMPATIBILITY: "1"
         run: |
           cd diffctx
           maturin build --release --out wheelhouse