service/state: Implement balance verification against AppHash

[renaynay]

Tl;dr, instead of requesting balance from core endpoint, the node now requests proofs as well and, using the proofs, verifies the returned balance against the AppHash of the corresponding block.

TODO:

• Implementation
• ADR to document use of ABCI query and proofs

Resolves #571.

Based on #910 , will rebase and mark as ready for review once merged.

[codecov-commenter]

Codecov Report

Merging #911 (2e3ccd5) into main (8d56e55) will decrease coverage by 0.40%.
The diff coverage is 19.54%.

@@            Coverage Diff             @@
##             main     #911      +/-   ##
==========================================
- Coverage   58.74%   58.34%   -0.41%     
==========================================
  Files         128      129       +1     
  Lines        7623     7727     +104     
==========================================
+ Hits         4478     4508      +30     
- Misses       2676     2750      +74     
  Partials      469      469              

Impacted Files	Coverage Δ
service/rpc/state.go	0.00% <0.00%> (ø)
service/state/helpers.go	0.00% <0.00%> (ø)
service/state/core_access.go	18.32% <10.00%> (-3.03%)	⬇️
node/components.go	90.69% <100.00%> (+0.33%)	⬆️
node/state/core.go	100.00% <100.00%> (ø)
node/state/state.go	100.00% <100.00%> (ø)
service/rpc/endpoints.go	100.00% <100.00%> (ø)
service/state/service.go	47.82% <100.00%> (+2.37%)	⬆️
node/config_opts.go	28.57% <0.00%> (-11.43%)	⬇️
header/core/listener.go	52.83% <0.00%> (-5.67%)	⬇️
... and 12 more

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[liamsi]

I only reviewed this from a high-level perspective and not line by line. I'm on-board with the decisions made (reflected in the ADR) and the high-level code seems fine.

[Wondertan]

Comments from sync review:

• Consolidate Balance methods with Verified methods(TBD in this PR)
• Wait until syncing is done before requesting balances and responding to the users(TBD in this PR)
  • Otherwise, users will get outdated balances during sync
• Take the latest pending Head from the Syncer and verify balances against it(Keeping it for later, needs an issue)
  • Pending headers are verified with known valset(within unbonding period) and safe to rely on
  • This way, users will be able to get balances(and other states) instantly, without waiting for sync to finish

[adlerjohn]

Where is verified_balance implemented? I don't actually see any code for that endpoint.

[renaynay]

@adlerjohn originally, I created a separate endpoint for verified balance, but after speaking with hlib, we decided to just replace the current balance endpoint with this verified one -- so a user requesting /balance will now get their balance returned (but it's now verified against the AppHash instead of being blindly returned)

[renaynay]

@Wondertan regarding unit test for ABCI query -- the problem here is again bottlenecked by simulating tendermint+app. It will be easy to tell by using the endpoint itself whether it is working or not. I know it's not ideal, but until we can simulate this pairing easily, it will be way more work than it's worth to do this test. The underlying methods used to prove membership are covered by tests inside ibc-go here.

Ref: #570