Improves the handling of channels and categories

[kjaffel]

This PR improves the handling of channels and categories to make the configuration more robust, faster, and less error-prone.
Changes:

• When certain channels are disabled, their corresponding categories are now skipped automatically.
• Channel names and IDs are kept in sync to avoid typos and mismatches.
  User-facing configuration via analysis.yaml
• Users no longer need to modify internal selection code.
  Instead, channels or categories can be enabled/disabled directly in analysis.yaml by commenting out the relevant entries:
  https://github.com/kjaffel/hhmultilepton2/blob/fixchannels_handling/multilepton/config/analysis.yaml#L325
• B-tag working points were previously hard-coded.
  They are now fetched from the correction library to ensure consistency and to automatically follow future working-point updates, avoiding silent mismatches:
  https://github.com/kjaffel/hhmultilepton2/blob/fixchannels_handling/multilepton/selection/lepton.py#L113-L114