Enable conditional dependencies and extras for user input

[jaimergp]

Needs:

• Consensus about syntax in CEP for the next evolution of Repodata (v2) and MatchSpec conda/ceps#111
• Support in conda is needed to process user-provided specs (CLI, environment files, etc): Conditional MatchSpec conda/conda#15443
• Bumping to py-rattler 0.20 or above Use conda>=25.5.0, py-rattler>=0.20, python>=3.10 #23

[jaimergp]

@danyeaw, FYI, if I disable the experimental_* flags in rattler.MatchSpec, the solver still processes the conditional dependencies found in the repodata just fine. To prove it:

$ python -m pytest -k test_conditional_specs      
================================================== test session starts ===================================================
platform darwin -- Python 3.10.19, pytest-9.0.2, pluggy-1.6.0 -- /Users/jrodriguez/devel/conda-rattler-solver/.pixi/envs/test-py310/bin/python
cachedir: .pytest_cache
rootdir: /Users/jrodriguez/devel/conda-rattler-solver
configfile: pyproject.toml
plugins: mock-3.15.1, timeout-2.4.0, xprocess-1.0.2, split-0.10.0, rerunfailures-16.1, cov-7.0.0
collected 142 items / 138 deselected / 4 selected                                                                        

tests/test_solver.py::test_conditional_specs_in_cli FAILED                                                         [ 25%]
tests/test_solver.py::test_conditional_specs_in_repodata_virtual PASSED                                            [ 50%]
tests/test_solver.py::test_conditional_specs_in_repodata_side1 PASSED                                              [ 75%]
tests/test_solver.py::test_conditional_specs_in_repodata_side2 PASSED                                              [100%]

Only the in_cli variant fails, as expected.