cmake: migrate Python module installation from setup.py to pip

cmake: migrate Python module installation from setup.py to pip

Replace 'setup.py install' with 'pip install --use-pep517' to fix
Cython compilation failures and eliminate deprecation warnings.

Problem Statement:
The build process for Cython modules involves preprocessing .pyx files
(e.g., generating rbd_processed.pyx from rbd.pyx) and then cythonizing
with specific compiler_directives. The previous approach using separate
'setup.py build' and 'setup.py install' commands caused this failure:

```
Error compiling Cython file:
------------------------------------------------------------
...
        """
        name = cstr(name, 'name')
        cdef:
            rados_ioctx_t _ioctx = convert_ioctx(ioctx)
            char *_name = name
            librbd_progress_fn_t _prog_cb = &no_op_progress_callback
                                            ^
------------------------------------------------------------

rbd_processed.pyx:781:44: Cannot assign type 'int (*)(uint64_t, uint64_t, void *) except? -1' to 'librbd_progress_fn_t'. Exception values are incompatible. Suggest adding 'noexcept' to type 'int (uint64_t, uint64_t, void *) except? -1'.
```

This occurs because:
1. 'setup.py build build_ext' successfully preprocesses and cythonizes
   with compiler_directives from setup.py's cythonize() call
2. 'setup.py install' internally triggers a rebuild that:
   - Regenerates the preprocessed .pyx files
   - Re-runs cythonize() through Cython.Distutils.build_ext
   - Does NOT apply the compiler_directives from setup.py
   - Fails on the regenerated files missing required directives

New Options Explained:

`--use-pep517`:
  Addresses deprecation warning:
  ```
    DEPRECATION: Building 'rados' using the legacy setup.py bdist_wheel
    mechanism, which will be removed in a future version. pip 25.3 will
    enforce this behaviour change.
  ```
  Uses the modern PEP 517 build backend which:
  - Performs a single build pass with all compiler_directives applied
  - Prevents the implicit rebuild that caused CompileError
  - Future-proofs against pip 25.3+ which will require this

`--no-build-isolation`:
  Ensures that environment variables set by CMake are respected:
  - CC, LDSHARED (compiler toolchain)
  - CPPFLAGS, LDFLAGS (compilation flags)
  - CYTHON_BUILD_DIR, CEPH_LIBDIR (build paths)

  Without this flag, pip would create an isolated build environment
  that ignores these critical build settings.

`--no-deps`:
  Prevents pip from attempting to install Python dependencies listed
  in setup.py's install_requires. All dependencies are managed by
  CMake and the distribution's package manager, not pip.

`--ignore-installed`:
  Addresses installation error when DESTDIR is set:
  ```
    ERROR: Could not install packages due to an OSError: [Errno 13]
    Permission denied: '/usr/lib/python3/dist-packages/rados-2.0.0.egg-info'

    OSError: [Errno 18] Invalid cross-device link:
    '/usr/lib/python3/dist-packages/rados-2.0.0.egg-info' -> '/tmp/pip-uninstall-...'
  ```
  This error occurs because pip detects an existing system installation
  and tries to uninstall it before installing to DESTDIR. With
  --ignore-installed, pip skips the uninstall step and directly installs
  to the DESTDIR staging directory, which is the correct behavior for
  packaging.

`--root-user-action=ignore`:
  In this change, we installing a python module using pip with
  `fakeroot` before packaging it. But pip warned:
  ```
  Error: WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behavior with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv
  ```
  But we use fakeroot on purpose, this option is added to silence this warning.

Removed Options:

`--install-layout=deb`:
  This Debian-specific patch to 'setup.py install' is no longer needed.
  Modern pip automatically detects the distribution and uses the correct
  layout (dist-packages on Debian, site-packages on RPM distros).

`--single-version-externally-managed`:
  This option was specific to 'setup.py install' to prevent egg
  installation. With pip, this is handled automatically.

`--record /dev/null`:
  No longer needed as pip manages installation records internally.

`egg_info --egg-base`:
  Not needed with pip as metadata is generated automatically during
  the build process.

New environmental variable:
`DEB_PYTHON_INSTALL_LAYOUT=deb` is conditionally applied when packaging
for debian-derivative distributions. As pip does not support
`--install-layout` option. Since debian patches pip so it installs Python
modules into /usr/local/lib instead of /usr/lib where debian dh_install
helper looks for the content to be packaged, so we have to enforce the
debian layout using the environmental variable.

Working Directory Change:

Changed from `CMAKE_CURRENT_SOURCE_DIR` to `CMAKE_CURRENT_BINARY_DIR` to
keep pip's temporary files and logs in the build directory rather than
polluting the source tree.

Additional Dependencies:

Since the build process uses pip and creates a wheel distribution,
we need to add `pip` and `wheel` Python modules as build dependencies.

Future Improvements

We considered implementing a custom `build_templates` command or using
setuptools' `sub_commands` mechanism to avoid regenerating `*_processed.pyx`
files on every build (tracking dependencies via file modification times or
hash-based checks). However, to keep `setup.py` simple and maintainable,
we've deferred this optimization for future work. The current solution
using `pip install --use-pep517` ensures correct builds without additional
complexity.

This solution works correctly for both Debian and RPM packaging workflows,
both of which use DESTDIR-based staged installations.

Fixes: 719b749846
Signed-off-by: Kefu Chai <k.chai@proxmox.com>