2. Route peer requests based on missing inventory

[teor2345]

Motivation

Zebra needs to stop asking the same peer for the same block multiple times.

Solution

• send inbound notfound messages to the inv collector
• use notfound inventory to route inventory requests in the peer set
• test that it all works

Part of #2156.

Review

@oxarbitrage is reviewing this PR.

Reviewer Checklist

• Code implements Specs and Designs
• Tests for Expected Behaviour
• Tests for Errors

Follow Up Work

• Security: Send notfound inv items to the inv collector, Credit: Equilibrium #2156
  • if a block or transaction request fails, times out, or is dropped, send a synthetic notfound message to the inv collector
• Make Zebra send notfound, and use received notfound to finish requests #2726
  • send notfound to peers when Zebra doesn't have a block or transaction
  • use received notfound to finish pending block or transaction requests

[codecov]

Codecov Report

Merging #3465 (95870a3) into main (499ae89) will decrease coverage by 0.01%.
The diff coverage is 73.95%.

@@            Coverage Diff             @@
##             main    #3465      +/-   ##
==========================================
- Coverage   78.34%   78.32%   -0.02%     
==========================================
  Files         267      273       +6     
  Lines       31526    31807     +281     
==========================================
+ Hits        24698    24914     +216     
- Misses       6828     6893      +65     

[oxarbitrage]

This looks good, i just have a minor question.