Function get_slope_distance 

fn get_slope_distance(
    ctx: &mut SpreadContext<'_>,
    pos: BlockPos,
    state: BlockStateId,
    depth: u8,
    from_direction: Option<Direction>,
    fluid_id: FluidRef,
    max_depth: u8,
) -> u16

Computes slope distance using DFS search.

Vanilla equivalent: FlowingFluid.getSlopeDistance(). Uses canPassThrough = canMaybePassThrough + canHoldSpecificFluid.