[python] Skip tests that use tiledb-py if not installed

[nguyenv]

Issue and/or context:

This PR is separated out from #2752

Changes:

Skip tests that use tiledb-py if not installed

[johnkerl]

@nguyenv thanks!!!

I'm putting this as request-changes just to put a "hold" on it -- no indication anything's necessarily wrong but rather to flag some things for conversation:

• Will we be doing pip-install of tiledb-py within our CI jobs?
  • If so: may need some (light) handling around core versions in the case when
    • Core has bumped storage-format version
    • TileDB-Py has that new core available at PyPI and TileDB-SOMA Py does not (or vice versa)
  • Also if so: that means the tests you have here may go "uncovered" for a while until we restore pip-install of tiledb-py within our CI YAML -- ok as long as we understand/track what we're doing
  • If not:
    • We'll be losing test coverage of assertions we once made and now no longer can
    • How bad is this?? Were these tests "extra" all along? Is this high-risk coverage or low-risk coverage we'd be losing?

Since the core C++ API (and C API) are "full APIs" that means anything we can/do do in TileDB-Py we should be able to do ourselves -- I want us to at least have the conversation about what to do with things like

            assert A.schema.sparse
            assert not A.schema.allows_duplicates
            assert A.dim("foo").filters == [tiledb.ZstdFilter(level=3)]
            assert A.attr("bar").filters == [tiledb.ZstdFilter()]

-- namely: can we either:

• Expose some of these things via libtiledbsoma -> pybind11/Rcpp -> tiledbsoma-py/tiledbsoma-r -> so we can still test them at the pytest level?
• Or, maybe expose something only at the libtiledbsoma level (no bindings) and then move these test cases from pytest (or testthat for R) to ctest for libtiledbsoma

[nguyenv]

My idea for the latter conerns: When creating a SOMAArray in C++, we can store the PlatformConfig that's passed in to generate the ArraySchema. Then have a platform_config getter that we can bind in the APIs. In Python, we could return that as a JSON formatted string.

So essentially your first bullet point.

[nguyenv]

I think we should install tiledb-py when running CI. We could have a requirements_ci.txt that pulls everything from requirements_dev.txt with just the additional requirement for tiledb. But yes we'd have to make sure the version of tiledb-py it pulls is compatible with the libtiledbsoma in tiledbsoma-py. I don't know how to deal with that yet but can look into it.

[johnkerl]

My idea for the latter conerns: When creating a SOMAArray in C++, we can store the PlatformConfig that's passed in to generate the ArraySchema. Then have a platform_config getter that we can bind in the APIs. In Python, we could return that as a JSON formatted string.

So essentially your first bullet point.

Hmm, I hadn't thought of that. TBH I don't think this is a good check -- it will be checking a copy of platform config stored somewhere, not checking against readback of the actual core schema that was created. We need to actually read the core schema and do these checks -- if we want to continue doing them at all ...