Refactor DeltaSpin PW subspace cache with std::vector - #8110

WARNING conda.conda_pypi.main:notify_externally_managed_future(156): Did you know? You can install many PyPI packages with conda using the conda-pypi beta. Get started: https://docs.conda.io/projects/conda/en/stable/new-features.html

The 'defaults' channel might have been added implicitly. If this is intentional, add 'defaults' to the 'channels' list. Otherwise, consider setting 'conda-remove-defaults' to 'true'.