[shared] Fix Clippy warnings in comm-opaque2

Summary:
Now we can do workspace-wide cargo clippy --workspace which produces lots of Clippy warnings.

Depends on D12174

Test Plan: cargo check -p comm-opaque2

Reviewers: varun

Reviewed By: varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12175