[FIX] Use library_dirs for cython linking, link cudatoolkit libs, allow setting UCX install location

[trxcllnt]

This PR is a continuation of #1694. Similar to rapidsai/cuml#4015, this PR updates setup.py to:

• Use library_dirs instead of runtime_library_dirs when linking Cython.
• Allow overriding UCX lib and include dirs via a UCX_HOME envvar.
• Link cudart, cusparse, and cusolver.

These are necessary to compile the Cython via pip when not inside a conda environment and when UCX is installed to a location other than /usr or /usr/local.

[codecov-commenter]

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[BradReesWork]

@gpucibot merge