➕ make strong_ptr transitive dependency + enhancements

[kammce]

• Make strong_ptr a transitive dependency
• Implement C++20 modules support with proper export declarations
• Update CMake configuration to use async_context-config.cmake and
  include EXPORT_PACKAGE_DEPENDENCIES
• Refactor async_context module to use export keywords for all
  types, classes, and enums
• Add test_package with CMakeLists.txt and conanfile.py for module
  testing
• Add .clangd configuration for better module development support
• Update conanfile.py to:
  • Include .cmake.in files in exports_sources
  • Use cmake/[^4.0.0] and ninja/[^1.3.0] as tool requirements
  • Update strong_ptr dependency to version 0.0.2 with transitive
    headers/libs enabled
• Remove std::function callback usage and replace with strong_ptr
  for scheduler interface to enable entire class objects as
  schedulers rather than just function wrappers
• Fix unit test execution by moving "Executing unit tests!" message
  to build phase and updating the test runner to use modern C++20
• Update async_context module to remove unused functional header
  and properly export all types and templates
• Add comprehensive test for coroutine double delay functionality
• Enhance scheduler test to properly handle chrono::nanoseconds
  type in variant