[safety feature] getHeader cutoff, don't return bids to proposer after that

[metachris]

📝 Summary

Don't return bids to proposer after 2 seconds into the slot (i.e. if they have a slow network connection)

---

✅ I have run these commands

• make lint
• make test-race
• go mod tidy
• I have seen and agree to CONTRIBUTING.md

[codecov-commenter]

Codecov Report

Merging #446 (9020b0c) into main (d729fa5) will not change coverage.
The diff coverage is 0.00%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@           Coverage Diff           @@
##             main     #446   +/-   ##
=======================================
  Coverage   29.06%   29.06%           
=======================================
  Files          24       24           
  Lines        4649     4649           
=======================================
  Hits         1351     1351           
  Misses       3110     3110           
  Partials      188      188           

Flag	Coverage Δ
unittests	29.06% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
services/api/service.go	34.53% <0.00%> (ø)