Consider adding Cython-based enum to the Sphinx documentation

[kingcrimsontianyu]

A new C++ enum kvikio::CompatMode will be exposed to Python API using Cython as of PR 547. However, Sphinx does not seem to be capable of processing the Cython code automatically, leaving this enum undocumented.

We may follow @wence- 's workaround initially devised for cuDF to generate Cython enum documentation for KvikIO.