Views on the evoland-plus data model

This file adds view active bindings and methods to the evoland_db class using R6's $set() method. These provide computed views on the database without storing additional data.

Active Bindings Added

• lulc_meta_long_v - Unrolled LULC metadata with one row per source class

• pred_sources_v - Distinct predictor URLs and their MD5 checksums

• transitions_v - Land use transitions derived from lulc_data_t

• extent - Spatial extent of coords_t as terra::SpatExtent

• coords_minimal - Minimal coordinate representation (id_coord, lon, lat)

Methods Added

• trans_pred_data_v(id_trans) - Returns wide table of transition results and predictor data for a specific transition. Used as input to covariance filtering.