Implement Neighbor Expansion Logic

[RobinGummels]

Description:
Implement Step 8: If more than 30% of pixels within a candidate cell are classified as snow/ice, mark all 4-neighboring cells (N, S, E, W) that haven't been processed yet as new candidate cells.

Tasks:

• Check if snow/ice percentage exceeds 30% threshold
• Identify 4-neighboring cells (North, South, East, West)
• Check which neighbors have NOT been processed yet
• Mark unprocessed neighbors as new candidates
• Add new candidates to processing queue
• Update is_candidate status in grid GeoDataFrame
• Track processing status per cell (processed/unprocessed/candidate)

Acceptance Criteria:

• Neighbor cells are correctly identified based on grid structure
• Only unprocessed neighbors are added as candidates
• No duplicate processing of cells
• Expansion logic is correctly triggered at 30% threshold
• Grid visualization updates to show new candidates