python: build a PyPI-publishable Pyodide (PEP 783) wheel

z3 already builds under Pyodide, but via `pyodide build` the resulting
wheel is tagged `emscripten_<pyodide-version>_wasm32` and only usable as a
CI artifact. PEP 783 introduced the portable `pyemscripten_<date>_wasm32`
tag that PyPI accepts and micropip can install at runtime. This makes z3
produce that wheel via `cibuildwheel --platform pyodide`.

Changes:

* setup.py: for the emscripten target, use the wheel platform tag that
  pyodide-build supplies verbatim via _PYTHON_HOST_PLATFORM (e.g.
  `pyemscripten_2026_0_wasm32`) instead of reconstructing an
  `emscripten_*` tag, falling back to the old behaviour when that env var
  is absent.

* setup.py / CMakeLists.txt / pyproject.toml: switch the Pyodide build
  from JS-based exceptions (`-fexceptions`, `-sDISABLE_EXCEPTION_CATCHING=0`)
  to native wasm exception handling (`-fwasm-exceptions
  -sSUPPORT_LONGJMP=wasm`), matching the ABI of the Pyodide 314 /
  emscripten 5 main module. With the old flags libz3.so imports `invoke_*`
  trampolines the runtime no longer provides, so the wheel builds but the
  first Z3 call fails at runtime with
  "Dynamic linking error: cannot resolve symbol invoke_vi".

* pyproject.toml: add [tool.cibuildwheel] / [tool.pyodide.build] config so
  `cibuildwheel --platform pyodide` builds and tests the wheel.

* add .github/workflows/pyodide-pypi.yml building the wheel with
  cibuildwheel and publishing it to PyPI (trusted publishing) on tags. The
  existing pyodide.yml artifact build is left unchanged.

Verified with cibuildwheel 4.1.0 / pyodide-build 0.35.0 / emscripten 5.0.3:
the resulting z3_solver-4.17.0.0-py3-none-pyemscripten_2026_0_wasm32.whl
passes z3test.py in the Pyodide runtime and solves SMT problems both under
node and in a browser via micropip.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/pyodide-pypi.yml

@@ -0,0 +1,57 @@
+name: Pyodide Wheel (PyPI)
+
+# Builds a PEP 783 `pyemscripten_*_wasm32` wheel for z3-solver using cibuildwheel
+# and publishes it to PyPI on tag pushes. Unlike the legacy pyodide.yml (which
+# uses `pyodide build` and produces a Pyodide-version-locked emscripten_* wheel
+# uploaded only as a CI artifact), this wheel is installable at runtime with
+# micropip from PyPI. See src/api/python/pyproject.toml [tool.cibuildwheel].
+
+on:
+  release:
+    types: [created]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  build-pyodide:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Build Pyodide wheel
+        uses: pypa/cibuildwheel@v4.1.0
+        with:
+          # The Python bindings live in a subdirectory of the repo.
+          package-dir: src/api/python
+        env:
+          CIBW_PLATFORM: pyodide
+          # Exception/longjmp/bigint flags are declared in
+          # src/api/python/pyproject.toml ([tool.pyodide.build]) and combined
+          # with Pyodide's -fwasm-exceptions defaults. Don't set CFLAGS/CXXFLAGS
+          # here — a JS-EH -fexceptions value conflicts with the wasm-EH ABI.
+
+      - name: Store Pyodide wheel
+        uses: actions/upload-artifact@v7
+        with:
+          name: pyodide-wheel
+          path: wheelhouse/*.whl
+
+  publish:
+    name: Publish to PyPI
+    runs-on: ubuntu-24.04
+    if: startsWith(github.ref, 'refs/tags/')
+    needs: [build-pyodide]
+    environment: release
+    permissions:
+      id-token: write  # trusted publishing (OIDC), no API token needed
+    steps:
+      - name: Download Pyodide wheel
+        uses: actions/download-artifact@v8
+        with:
+          name: pyodide-wheel
+          path: dist/
+
+      - name: Publish to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1