Function sync15::state::is_same_timestamp

fn is_same_timestamp(
    local: ServerTimestamp, 
    collections: &InfoCollections, 
    key: &str
) -> bool

Whether we should skip fetching an item. Used when we already have timestamps and want to check if we should reuse our existing state. The state's fairly cheap to recreate and very bad to use if it is wrong, so we insist on the exact timestamp matching and not a simple "later than" check.