refactor(level0): rename date_obs parameter to obs_date

- Changed date_obs to obs_date in find function signature
- Updated date_obs_start and date_obs_end keys to obs_date_start and obs_date_end
- Modified prc_time parameter to prc_date in find_process and add_process functions
- Adjusted related logic to use obs_date and prc_date consistently
- Updated test cases to reflect the parameter name changes