Make NodeLink a Modular Installable Library

[icypress99]

Description:
Currently, NodeLink requires users to include the full source code in their projects. To improve usability and integration, we should refactor NodeLink so that it can be installed as a module, similar to QtMqtt. This will allow users to link against it via find_package(NodeLink REQUIRED) and target_link_libraries(MyProject PRIVATE NodeLink) without copying the entire source code.

Additionally, all example projects and demos should be updated to use the new modular approach.

Acceptance Criteria:

• NodeLink can be installed as a system or project library (via CMake install and find_package).
• Existing examples updated to link against NodeLink as a module rather than including source code.
• Documentation updated to show installation and usage instructions for modular integration.
• Ensure backward compatibility where possible or document breaking changes.
• Tests/examples should build and run correctly using the modular setup.

Technical Notes:

• Consider using CMake EXPORT targets for proper modular linking.
• Review how QtMqtt handles modular CMake installation for reference.
• Update CMakeLists.txt in the root and examples directories.
• Ensure proper versioning and namespace management.