Add effect and marker initialization to Clip

[peter-targett]

Summarize your change.

Extend Clip to allow effects and markers to be set, matching how Gap's can be initialized.

Reference associated tests.

Added basic C++ and Python tests.

[jminor]

Thanks for the update. Your change looks good to me. There's a build failure which I think is unrelated to your change. Let me see if we can find someone to help with that.

    File "/tmp/pip-build-env-hksa4rl4/overlay/lib/python3.9/site-packages/setuptools/_distutils/command/build_ext.py", line 502, in _build_extensions_serial
      self.build_extension(ext)
    File "<string>", line 70, in build_extension
    File "<string>", line 85, in build
    File "<string>", line 166, in cmake_preflight_check
  RuntimeError: CMake Error: Could not find CMAKE_ROOT !!!
  CMake has most likely not been installed correctly.
  Modules directory not found in
  /tmp/pip-build-env-hksa4rl4/overlay/share/cmake-3.31
  CMake Error: Error executing cmake::LoadCache(). Aborting.
  error: subprocess-exited-with-error

[peter-targett]

This could be a separate pull request, I note the order of the arguments between gaps and clips could be more aligned.