Function parse_partition_dir_name 

pub fn parse_partition_dir_name(name: &str) -> Option<PartitionDirName>

Reads back the partition that partition_dir_name rendered.

The name is parsed from the right, because a topic name may contain - while neither the partition index nor the fixed-width topic id can. Returns None when a component is absent or malformed, which includes a topic that is empty or that holds the / key separator.