feat: add valset injection through r/sys/validators

[zivkovicmilos]

Description

This PR introduces an EndBlocker system for applying validator set changes protocol level, based on on-chain events (from the /r/sys/vals realm).

I've utilized an already existing system:

• validator set changes still stay managed protocol-level in ConsensusState -> refactoring this is not a small feat, and saying this is an understatement
• event switch utilized by the node that dumps new block / new transaction events

The way this flow essentially works is the following:

1. An on-chain event happens that indicates a change in the validator set (added / removed)
2. These events (ABCI events) are parsed as soon as they end up in a transaction result (are pushed to the event system of the SDK). The top-level ABCI event type needs to beEventTx (indicating it's a new TX result). The underlying tx GnoVM events (GnoEvent) need to be from the /r/sys/validators Realm, and be a validator addition / removal (type defined in the Realm)
3. Events are parsed down into abci.ValidatorUpdates, which are returned as a result of EndBlocker
4. This EndBlocker result is later read by the ConsensusState, and the validator set changes are applied for the upcoming block in a series of existing callbacks. This also keeps proposer priority logic in check.

Blocked by #2130
Closes #1823

---
title: on-chain validator set injection flow
---
flowchart TD
    subgraph app.go
        nesvw(["Node event switch"]) -. pass all block events .-> collector(["event collector"])
        collector -. subscribes to .-> nesvw

        collector -. filter new events .-> collector

        EB["func EndBlocker(...)"] == 1: fetch relevant events ==> collector
        collector -. 2: return events, if any .-> EB
    end

    subgraph gno.land/r/sys/validators.gno
        GC["func GetChanges(from int64) []validators.Validator"]

        addVal["func addValidator(...)"]
        removeVal["func removeValidator(...)"]
        PE["func NewPropExecutor(changesFn) proposal.Executor"]

        PE -. calls internally .-> addVal
        PE -. calls internally .-> removeVal

        addVal -. std emits ValidatorAdded .-> nesvw
        removeVal -. std emits ValidatorRemoved .-> nesvw
    end

    subgraph gno.land/r/gov/dao.gno
        EP["func ExecuteProposal(...)"]
        

        EP == executes on-chain ==>PE
    end

    subgraph user_proposal.gno
        main("func main() {...}")
        PR["govdao.Propose(...)"]

        main -. contains .-> CB
        main -. contains .-> PR

        CB("changesFn func() []validators.Validator {...}")

        CB== creates ==>PE
        CB("changesFn func() []validators.Validator {...}")

        PE == passed into ==> PR
    end

    A[/fa:fa-user User\] == gnokey maketx run ==> main
    GDV[/fa:fa-people-group GOVDAO members\] == manually call ==> EP

    EB == 3: execute VM call to get changes since last block ==> GC
    GC -. 4: return changes .-> EB

    EB -. 5: return response with valset changes .-> EBR([abci.ResponseEndBlock]) -- applied in --> AB
    subgraph Cosmos SDK
        AB["func ApplyBlock(...) {...}"]
    end

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Related: #1945

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

Attention: Patch coverage is 63.15789% with 42 lines in your changes missing coverage. Please review.

Project coverage is 54.92%. Comparing base (b1d778c) to head (abc2fc1).

Files	Patch %	Lines
gno.land/pkg/gnoland/app.go	55.55%	24 Missing and 4 partials ⚠️
gno.land/pkg/gnoland/vals.go	43.75%	6 Missing and 3 partials ⚠️
gno.land/pkg/gnoland/node_inmemory.go	0.00%	4 Missing ⚠️
gnovm/stdlibs/std/emit_event.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2229      +/-   ##
==========================================
+ Coverage   54.88%   54.92%   +0.03%     
==========================================
  Files         592      594       +2     
  Lines       79232    79297      +65     
==========================================
+ Hits        43487    43550      +63     
+ Misses      32460    32455       -5     
- Partials     3285     3292       +7     

Flag	Coverage Δ
contribs/gnodev	23.53% <100.00%> (+0.38%)	⬆️
contribs/gnofaucet	14.46% <ø> (ø)
contribs/gnokeykc	0.00% <ø> (ø)
contribs/gnomd	0.00% <ø> (ø)
gno.land	63.14% <59.80%> (+0.25%)	⬆️
gnovm	60.21% <80.00%> (ø)
tm2	54.45% <100.00%> (+0.01%)	⬆️

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[moul]

Approving, but please follow the suggestions.

[moul]

I believe this approach is preferable 👍

You'll likely find this the most advanced use of avl you've encountered so far.
My previous comments were merely suggestions on how to potentially maximize the utilization of avl features. I hope you find this helpful.