CI: modernize the OpenCL Python-package wheel jobs (setup.py → pyproject, drop cp37/cp38)

The `*-opencl-python-packages` CI jobs in `.github/workflows/build-test-package.yml` are red and need a coordinated modernization. These failures are independent of the C++/CUDA build (which is green on all platforms after #77) and were long masked while every run aborted at the retired GitHub Actions cache service.

Two root causes

**1. The wheel build script calls `python setup.py`, but the module is `pyproject.toml`-only.**
`itk-python-package-tag: 03391ad738438661fff40bfe37a7cfabd171b9b1` pins an ITKPythonPackage `manylinux-build-module-wheels.sh` that invokes `python setup.py …`. The module ships only `pyproject.toml` (scikit-build-core), so the build fails:
```
/opt/python/cp38-cp38/bin/python: can't open file 'setup.py': [Errno 2] No such file or directory
```

**2. The `python-version` matrix still lists cp37/cp38, which ITK 5.4 dropped.**
After #77 bumped `itk-wheel-tag` to `v5.4.6` (to match the C++ build's ITK), the ITKPythonBuilds cache no longer contains 3.7/3.8 wheels (ITK 5.4 requires Python ≥3.9), so extraction fails:
```
tar: ITKPythonPackage/ITK-cp38*: Not found in archive
```

Proposed fix

- Drop `"37"` and `"38"` from every `python-version` matrix in `build-test-package.yml` (linux/windows/macos package jobs); ITK 5.4 supports Python ≥3.9.
- Bump `itk-python-package-tag` to an ITKPythonPackage commit whose `manylinux-build-module-wheels*.sh` builds `pyproject.toml` projects (no `setup.py` invocation), or add a thin `setup.py` shim if a compatible tag isn't available.
- Keep `itk-wheel-tag` aligned with the C++ build's `itk-git-tag` (currently `v5.4.6`).
- Re-validate `build-linux/windows/macos-opencl-python-packages` and `publish-python-packages-to-pypi`.

Affected jobs

`build-linux-opencl-python-packages (37/38/39/310/311)`, `build-macos-opencl-python-packages`, `build-windows-opencl-python-packages (9/10/11)`.