Function vshard_for_array_coord 

pub fn vshard_for_array_coord(
    array_name: &str,
    coord: &[u64],
    tile_extents: &[u64],
) -> u32

Compute the vShard ID for an array op at the given coordinate.

The shard key is array_name_bytes || tile_id.to_le_bytes(), hashed via vshard_from_key.

Falls back to array_vshard_for_name(array_name) when:

• coord / tile_extents are empty or mismatched.
• Any tile_extents[i] is zero.

Returns a raw u16 in 0..1023. Callers wrap it in VShardId::new(…).