ci: use CC/CXX=sccache cl on Windows to cache DuckDB C++ builds

CC_WRAPPER didn't work because the cc crate doesn't check that env var.
The real issue: when the cc crate finds MSVC cl.exe via find_msvc_tools,
it bypasses the RUSTC_WRAPPER-based sccache fallback that works on Linux.

Setting CC/CXX='sccache cl' on Windows makes the cc crate's env_tool
parser recognize "sccache" as a known wrapper and "cl" as the compiler.
This routes the ~21-minute libduckdb-sys C++ build through sccache.

First run will still be slow (cache seeding), but subsequent runs should
see C/C++ cache hits and significantly faster Windows builds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: cpsievert

.github/workflows/python.yml

@@ -42,9 +42,12 @@ jobs:
           args: --release
           sccache: true
         env:
-          # Ensure the cc crate routes C/C++ compilations (e.g. DuckDB)
-          # through sccache on all platforms, including Windows/MSVC
-          CC_WRAPPER: sccache
+          # On Windows/MSVC, the cc crate's cl.exe detection bypasses its
+          # RUSTC_WRAPPER-based sccache fallback. Setting CC/CXX explicitly
+          # makes the cc crate parse "sccache" as a known wrapper and "cl"
+          # as the compiler, routing DuckDB C++ builds through sccache.
+          CC: ${{ runner.os == 'Windows' && 'sccache cl' || '' }}
+          CXX: ${{ runner.os == 'Windows' && 'sccache cl' || '' }}
 
       - name: Upload wheel
         uses: actions/upload-artifact@v4