Improve Boost Python component detection for CMake-based Boost installs

[idesign0]

This PR improves the CMake logic used to locate Boost.Python in cv_bridge.

Recent Boost versions (e.g. 1.89) built with CMake no longer generate
versioned CMake package config files for Python components such as:

boost_python311-config.cmake

Instead, the only available package config file is the generic component:

boost_python-config.cmake

This causes the current logic:

    find_package(Boost REQUIRED COMPONENTS python${Python3_VERSION_MAJOR}${Python3_VERSION_MINOR})
    set(boost_python_target "Boost::python${Python3_VERSION_MAJOR}${Python3_VERSION_MINOR}")

to fail even though the library file libboost_python311.* exists.

Cause

CMake-built Boost installs:

• libboost_python<pyver>.*
• a generic CMake target: Boost::python

But does not install:

• Boost::python${Python3_VERSION_MAJOR}${Python3_VERSION_MINOR}
• boost_python${Python3_VERSION_MAJOR}${Python3_VERSION_MINOR}-config.cmake

As a result, CMake cannot resolve the requested versioned component, and the
configuration step fails even though the underlying library file exists.

CMake Side FIx

Use versioned Boost.Python components when available, and automatically fall back to the generic python component when they are not.
This makes the CMake logic compatible with both CMake-built and Autotools-built Boost installations.