[FEA] Implement new test organization in cuDF

[vyasr]

Is your feature request related to a problem? Please describe.
#12288 created a new organization for Python tests to handle the request in #4730. The intent was to migrate tests to the new directories over time. However, soon after #12288 merged our focus shifted substantially towards the cudf.pandas effort, and now the cudf.polars and pylibcudf projects. As a result, the transition to a new testing organization remains largely incomplete. The combined work around the pylibcudf backend and the polars/pandas frontends already requires a fairly thorough revamping of tests. We are writing new pylibcudf tests with each PR now, and we are adding cudf tests as we go. Some of the old tests, particularly of cudf's column layer, are likely to become obsolete as we rearchitect the internals around pylibcudf. As this process proceeds, we may lose track of how we want the cudf tests reorganized.

Describe the solution you'd like
The next time that we have a tech debt-focused release of cudf, we should consider doing some wholesale migrations and cleanup of tests to get rid of unnecessarily duplicated tests and move tests into the final destinations that we want.