`fremor run`: Update core CMORization logic for CMIP6Plus

[ilaflott]

Description: Ensure fremor correctly passes CMIP6Plus resources to the underlying C-based cmor library.

• Modify internal dataset.json writer to point outpath and table_id to the new mip-cmor-tables directory.
• Inject the exact path of the downloaded CMIP6Plus_CV.json into the cmor.setup() initialization.
• Add pre-validation logic to strictly check user configuration attributes (activity_id, experiment_id, source_id, institution_id) against the CV arrays before execution to prevent C-level segfaults.

[ilaflott]

this was at least partially addressed by #187