[rust] Fix Clippy warnings about DateTime
Summary:
Received a warn that the chrono::NaiveDateTime::from_timestamp is deprecated. Replaced this with recommended method which also simplified our code
Depends on D12176
Test Plan:
- cargo check
- CI - there are some unit and integration tests that rely on timestamps
Reviewers: varun
Reviewed By: varun
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D12178