pybind: switch from pkgutil.find_loader() to importlib.util.find_spec()

Replace pkgutil.find_loader() with importlib.util.find_spec() throughout
Python bindings. This addresses the deprecation warning in Python 3.10
(scheduled for removal in 3.14) that appeared when generating librbd
Python bindings.

The importlib.util.find_spec() API has been available since Python 3.4
and is compatible with our minimum required Python version (3.9, since
commit 51f71fc).

The warning resolved:
```
/home/kefu/dev/ceph/src/pybind/rbd/setup.py:8: DeprecationWarning: 'pkgutil.find_loader' is deprecated and slated for removal in Python 3.14; use importlib.util.find_spec() instead
  if not pkgutil.find_loader('setuptools'):
```

Signed-off-by: Kefu Chai <[email protected]>

Author: tchaikov

src/pybind/cephfs/setup.py

@@ -1,11 +1,11 @@
 import os
-import pkgutil
+import importlib.util
 import shutil
 import subprocess
 import sys
 import tempfile
 import textwrap
-if not pkgutil.find_loader('setuptools'):
+if not importlib.util.find_spec('setuptools'):
     from distutils.core import setup
     from distutils.extension import Extension
 else:

src/pybind/rados/setup.py

@@ -1,5 +1,5 @@
-import pkgutil
-if not pkgutil.find_loader('setuptools'):
+import importlib.util
+if not importlib.util.find_spec('setuptools'):
     from distutils.core import setup
     from distutils.extension import Extension
 else:

src/pybind/rbd/setup.py

@@ -1,11 +1,11 @@
 import os
-import pkgutil
+import importlib.util
 import shutil
 import subprocess
 import sys
 import tempfile
 import textwrap
-if not pkgutil.find_loader('setuptools'):
+if not importlib.util.find_spec('setuptools'):
     from distutils.core import setup
     from distutils.extension import Extension
 else:

src/pybind/rgw/setup.py

@@ -1,5 +1,5 @@
-import pkgutil
-if not pkgutil.find_loader('setuptools'):
+import importlib.util
+if not importlib.util.find_spec('setuptools'):
     from distutils.core import setup
     from distutils.extension import Extension
 else: