fix: populate sha256 in resource files and fix Windows PythonConfiguration

- Add sha256 field to Windows PythonConfiguration (PyPy/GraalPy have
  direct download URLs on Windows too)
- Pass sha256 to install_pypy() and install_graalpy() in windows.py
- Fix update_pythons.py: handle empty sha256 from CPython API (older
  versions) by streaming download to compute it; fix condition to
  check 'not sha256' rather than 'not in dict'
- Fix update_virtualenv.py: compute sha256 even when version unchanged
  but sha256 is empty (first-time population)
- Fix update_python_build_standalone.py: resolve file path relative to
  the script itself (not the installed package) so writes go to source
  checkout, not the uv cache
- Populate actual sha256 values by running all three update scripts

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Assisted-by: copilot-cli:claude-sonnet-4.6

bin/update_python_build_standalone.py

@@ -11,6 +11,8 @@
 # ///
 
 import json
+from pathlib import Path
+from typing import Final
 
 import requests
 
@@ -19,7 +21,13 @@ from cibuildwheel.util.python_build_standalone import (
     PythonBuildStandaloneAsset,
     PythonBuildStandaloneReleaseData,
 )
-from cibuildwheel.util.resources import PYTHON_BUILD_STANDALONE_RELEASES
+
+# Resolve path relative to this script so writes go to the source checkout,
+# not the uv-installed copy of the package.
+DIR: Final[Path] = Path(__file__).parent.parent.resolve()
+PYTHON_BUILD_STANDALONE_RELEASES: Final[Path] = (
+    DIR / "cibuildwheel/resources/python-build-standalone-releases.json"
+)
 
 
 def main() -> None: