Convert block/header sync timeouts to std::chrono types

Summary:
Partial backport of core#21015:
https://github.com/bitcoin/bitcoin/pull/21015/commits/c733ac4d8a597b1001555b142f488ed9fbecc405

Depends on D10903.

Ref T1696.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Maniphest Tasks: T1696

Differential Revision: https://reviews.bitcoinabc.org/D10906