Build sdist in split-package mode so its metadata matches the wheels (k2-fsa#3690)

The published wheels are built with SHERPA_ONNX_SPLIT_PYTHON_PACKAGE=ON,
so their metadata declares `sherpa-onnx-core==<version>`. The sdist, however,
is built without that variable, so `need_split_package()` returns False and
`install_requires` becomes None -- the sdist's Requires-Dist omits
sherpa-onnx-core entirely.

Tools that resolve dependencies from sdist metadata (notably `uv lock`)
therefore produce a lockfile without sherpa-onnx-core. After `uv sync`,
only sherpa-onnx is installed and `import sherpa_onnx` fails with a missing
libonnxruntime dylib, even though a direct `uv pip install` works.

Setting SHERPA_ONNX_SPLIT_PYTHON_PACKAGE=ON for the sdist build makes the
sdist's metadata declare the same core dependency as the wheels.

Fixes k2-fsa#3689

Co-authored-by: Eridanus117 <eridani117@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/build-wheels-linux.yaml

@@ -425,6 +425,12 @@ jobs:
       - name: Build sdist
         if: matrix.python-version == 'cp38' && matrix.manylinux == 'manylinux2014'
         shell: bash
+        env:
+          # Build the sdist in split-package mode so its metadata declares the
+          # sherpa-onnx-core dependency, matching the published wheels. Without
+          # this, the sdist's Requires-Dist omits sherpa-onnx-core, which breaks
+          # tools that resolve from sdist metadata (e.g. `uv lock`). See #3689.
+          SHERPA_ONNX_SPLIT_PYTHON_PACKAGE: ON
         run: |
           python3 setup.py sdist
           ls -l dist/*