2. fix(state): Make FindHeaders and FindHashes run concurrently with state updates

[teor2345]

Motivation

Zebra reads 160 headers for each FindHeaders request.
The FindHeaders requests used to take 5-10 seconds to answer, they might still be a bit slow.

So we want to run them concurrently with state updates.

Depends-On: #4825

Solution

• Make FindHeaders and FindHashes run concurrently with state updates
  • Use the new methods in existing state methods
• Make some state queries more efficient

Review

This is an urgent PR to fix Zebra sync performance.

Reviewer Checklist

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

[codecov]

Codecov Report

Merging #4826 (032c6a4) into main (ed553a9) will decrease coverage by 0.09%.
The diff coverage is 79.64%.

@@            Coverage Diff             @@
##             main    #4826      +/-   ##
==========================================
- Coverage   78.88%   78.78%   -0.10%     
==========================================
  Files         305      305              
  Lines       38559    38733     +174     
==========================================
+ Hits        30418    30517      +99     
- Misses       8141     8216      +75     

[teor2345]

In my local tests, PRs #4825 and #4826 make all FindBlockHeaders requests complete in under 5 seconds.
(Our current performance logging limit.)

[oxarbitrage]

Looks good.

[teor2345]

I rebased this branch on the squashed commit.

All the tests passed except lightwalletd (PR #4828) and mempool_transaction_expiration (ticket #4819), so I'm going to admin-merge this PR.