executor: add TiCIVectorQueryInfo for hybrid vector queries (#405)

Add TiCIVectorQueryInfo protobuf message to support TiCI hybrid index
vector search. This enables TiDB planner to push down vector top-k
queries through the TiCI path instead of the legacy ANN path.

Changes:
- Add TiCIVectorQueryInfo message with index_id, column_id,
  distance_metric, top_k, query_vector, dimension, filter_expr,
  and column_name fields.
- Add tici_vector_query_info field to IndexScan (field 8).
- Add TiCI vector scan context metrics to TiFlashScanContext
  (fields 200-205).
- Regenerate Go code.

Author: kolafish