Refactor Parpulse based on #50

[lanlou1554]

1. make pin_count a field of ReplacerValue since it'll be used by all replacers
2. for notify in mod.rs in memdisk, implement sth like this would introduce less complexity and make the code easier to write & maintain? (we can remove .0 and .1, also wrap code)
   https://github.com/kaimast/tokio-condvar/blob/main/src/lib.rs

see details in #50