Function vshard_for_array_tile 

pub fn vshard_for_array_tile(array_name: &str, tile_id: u64) -> u32

Compute the vShard ID for an array tile by tile identifier.

Use this when the tile_id is already known (e.g. from the op-log key or snapshot metadata) and coord re-derivation is unnecessary.

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