VSN-1976/ Fix time slot heights for overlapping slots in calendar cells for Affected journey

Corrected the height calculation of slots in calendar cells for 'Trajet affecté'

Previously, slots used totalMaxHeight or overlappingGroups.length to determine their height, which caused single slots to take full cell height and overlapping slots to sometimes overlap visually.

Changes:

• Compute the height per slot based on its own overlapping group size.
• Calculate slot top position according to its index within its group.
• Ensure single slots take full cell height, overlapping slots take SLOT_HEIGHT.
• Apply same logic for driver slots, absences, and non-affected slots.

This fixes visual overlapping issues and ensures proper stacking of slots.