[lib] Handle replies count

Summary:
Check if a message should be counted in replies count and generate appropriate updates.

https://linear.app/comm/issue/ENG-8892/handle-replies-count-as-a-part-of-dmoperationspecs

Depends on D12881

Test Plan: Just the Flow. Further testing will be performed after it is connected with the rest of the app.

Reviewers: kamil, inka

Reviewed By: inka

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12921