feat: add cadcat_preview catalog for sup3rcc preview datasets

[neilSchroeder]

Summary of changes and related issue

Adds a new 'cadcat_preview' catalog alongside cadcat, renewables, and hdp for internal/pre-release datasets. First member is sup3rcc (NREL super- resolved 4km CONUS data; EC-Earth3-CC historical + ssp245, 13 variables).

• New CATALOG_CADCAT_PREVIEW constant and CADCAT_PREVIEW_CATALOG_URL path
• Bundled intake-esm collection (cae-preview-collection.json + cae-preview-zarr.csv) under climakitae/data/; resolved via _package_file_path at load time. The URL may later be flipped to an s3:// URL so AWS credentials gate access.
• DataCatalog loads preview with silent failure (logger.debug) so users without access to internal data see no warnings; adds .preview property and merge_catalogs inclusion mirroring HDP/renewables patterns.
• New CadcatPreviewValidator opts out of warming_level, bias_adjust_model_to_station, and filter_unadjusted_models processors (cadcat/WRF/LOCA2-specific). Uses the same activity_id/table_id/grid_label/variable_id required keys.
• variable_descriptions.csv: 9 sup3r-unique vars (swddif, swddni, swdnb, wd10/100/200, ws10/100/200). Shared vars (t2, prec, psfc, rh) reuse existing Dynamical rows via first-match lookup semantics.
• 15 new validator tests + updated data_access tests for the 4th catalog.

Testing

• Unit tests written for new/modified code (goal: 80% coverage)
  • All public functions have unit tests
  • Functions that must produce specific values have unit tests
• Verified that notebooks utilizing affected functions still work
• Appropriate manual testing completed
• Advanced Testing label added to PR if this PR makes major changes to the codebase

How to Test

sup3r_preview_demo.ipynb
Download this notebook ^, checkout this branch and install locally with pip install -e ., then play around with loading and manipulating the Sup3rCC dataset with climakitae.

Documentation

• Complex code includes comments explaining logic
• Function documentation created (docstrings)

Code Quality

• Follows PEP8 naming and style conventions
• Helper functions prefixed with underscore _
• Linting completed and all issues resolved
• Does not replicate existing functionality
• Aligns with general coding standards of existing codebase
• Code generalized for multiple uses (unless too complex/time-intensive)

Review Process

• PR review instructions provided:
  • Type of review requested (scientific/technical/debugging)
  • Level of review detail needed

Administrative Reminders

• Jira ticket moved to "Review" when PR created
• Jira ticket will be moved to "Done" when complete
• PR branch will be deleted after merge