fix(cmake): standardize exported target name to container_system::container_system

[kcenon]

What

Summary

Standardize the CMake exported target name from container_system::container to
container_system::container_system, following the <package>::<package> convention.

Change Type

• Bugfix (fixes an issue)

Affected Components

• CMakeLists.txt - Changed EXPORT_NAME and added canonical alias
• cmake/container_system-config.cmake.in - Added backward compatibility alias

Why

Problem Solved

After find_package(container_system), consumers previously got
container_system::container instead of the conventional
container_system::container_system. This deviates from the standard
<package>::<package> naming convention used by most CMake packages.

Related Issues

• Part of fix: standardize CMake exported target naming conventions vcpkg-registry#78

Where

Files Changed

File	Type of Change
CMakeLists.txt	Changed EXPORT_NAME, added canonical alias
cmake/container_system-config.cmake.in	Added alias + updated target references

How

Implementation Details

1. Changed EXPORT_NAME from container to container_system in
   set_target_properties() so the exported target becomes
   container_system::container_system.

2. Added container_system::container_system as a build-tree alias for
   in-tree consumers (unified builds).

3. Added a backward-compatible alias in the config template:

   if(NOT TARGET container_system::container)
       add_library(container_system::container ALIAS container_system::container_system)
   endif()

4. Updated ContainerSystem::container legacy alias to link against
   container_system::container_system instead of container_system::container.

5. Updated container_system_LIBRARIES variable to use the new canonical name.

Breaking Changes

None - existing consumers using container_system::container or
ContainerSystem::container will continue to work via backward-compatible aliases.

[github-actions]

Performance Benchmark Report

Summary

• Total benchmarks: 0
• Regressions: 0 ✅
• Improvements: 0
• Unchanged: 0 (within 10% threshold)

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✅ Status: No significant performance regressions detected.