Refactor `sits_classify.vector_cube()` to conform new OBIA requirements

[rolfsimoes]

Describe the requested improvement

The old segment-based classification behavior in sits_classify.vector_cube() is deprecated.

When the input is a segs_cube (inherits from vector_cube + raster_cube), sits_classify() now follows the standard raster classification workflow. It applies the temporal model, produces pixel-level probabilities, preserves vector_info, and returns a probs_vector_cube.

Segment-level aggregation is no longer performed in sits_classify().

Associated sits API function

This affects sits_classify(), specifically the S3 method for vector_cube.

Expected behavior, reflecting the actual S3 class:

segs_cube (vector_cube + raster_cube)
  -> sits_classify()
probs_vector_cube (derived_vector_cube + segs_cube)

• No new parameter is required.
• The parameter n_sam_pol, previously used for the old vector classification workflow, emits an explicit deprecation warning:

"Parameter 'n_sam_pol' is deprecated. Segment-level classification is no longer performed by sits_classify(). Segment-based aggregation belongs to sits_label_classification()."

Additional context

• sits_classify() remains responsible for temporal probabilistic classification.
• Segment-based class assignment is handled later, during labeling.
• The output preserves vector_info; the resulting probability cube can still be labelled or analysed using the associated segments.