fix(sync): Make timeouts shorter to reduce full sync times

[teor2345]

Motivation

The full sync is timing out, so we want to reduce the amount of time we wait for stuck blocks.

Solution

Reduce the default block timeout to 8 minutes, and the final checkpoint timeout to 2 minutes.

Review

@arya2 is also working on fixing this.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
• How do you know it works? Does it have tests?

Follow Up Work

Increase the Rust test or workflow job timeouts, if needed.

[teor2345]

macOS tests failed due to a network error and bug #4649:

assertion failed: output.stdout_line_contains("activating mempool").is_err()

https://github.com/ZcashFoundation/zebra/actions/runs/3237875279/jobs/5305448541#step:15:520

[codecov]

Codecov Report

Merging #5397 (32a25a1) into main (8e5425f) will increase coverage by 0.00%.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5397   +/-   ##
=======================================
  Coverage   79.10%   79.11%           
=======================================
  Files         308      308           
  Lines       39752    39752           
=======================================
+ Hits        31447    31449    +2     
+ Misses       8305     8303    -2