Simplify/clarify watchdog code

- Use Debug trait object rather than arbitrary closure
- Combine bool+Instant into Option<Instant>
- Disambiguate "timeout"
- Add comments
- Simplify multi-argument matches

Test: keystore2_test
Test: libwatchdog_rs.test
Flag: None, refactor
Change-Id: Ieb16257c763fc2e04d592d97f341fea27aad726f
5 files changed