Add Verification + Tracking Logic To Simplex Blocks

[samliok]

Why this should be merged

In addition to calling Verify on the blocks inner vmBlock, we need to do some additional checks to ensure a simplex block can be verified. Furthermore, we need to ensure that any verified blocks are eventually accepted or rejected.

How this works

In simplex we do some pre-verification logic. However this is not enough, as we do not have access to the inner vmBlock pointed to by the prev field in the ProtocolMetadata. This means our verification logic in avalanchego must verify that prev for the block we are currently verifying points to that blocks parent. To understand more about why this important, see this test.

This PR also introduces a blockTracker struct to keep track of blocks that have been verified. When index is called on a digest, the blockTracker calls Accept on that block and Reject on any competing blocks.

How this was tested

Need to be documented in RELEASES.md?

[Copilot]

Pull Request Overview

This PR refactors change tracking in the Merkle DB view and history layers, replacing the old keyChanges+sortedKeys approach with a unified values map and a new recordValueChange method. It also updates the view iterator to reflect the map-based storage and overhauls history retrieval functions to collapse and filter changes via the new map structure.

• Replaces keyChanges and sortedKeys with values map and recordValueChange in view.go
• Updates NewIteratorWithStartAndPrefix to iterate over values and then sort the results in view_iterator.go
• Refactors history functions (getValueChanges, getChangesToGetToRoot) to use the new map-based change summary in history.go and updates tests

Reviewed Changes

Copilot reviewed 89 out of 91 changed files in this pull request and generated 1 comment.

File	Description
x/merkledb/view.go	Introduced recordValueChange method and values map
x/merkledb/view_iterator.go	Changed iterator to range over values and sort KeyChanges
x/merkledb/history.go	Refactored history change accumulation to use changeSummary
x/merkledb/history_test.go	Updated tests to assert on values instead of slices

Comments suppressed due to low confidence (2)

x/merkledb/view_iterator.go:27

• [nitpick] The local variable changes shadows v.changes and may be confusing. Consider renaming it to something like result or filteredChanges.

		changes   = make([]KeyChange, 0, len(v.changes.values))

[yacovm]

I think we need to grab the context lock here, because we're executing this function asynchronously.

I think that there is something I overlooked, please see comment.