fix(contracts): OZ-L07 Potentially Misleading Verifier Event

[zimpha]

Purpose or design rationale of this PR

This PR partially fixed the issue reported by Openzepplin (L-07 Potentially Misleading Verifier Event). The following are the details:

The MultipleVersionRollupVerifier contract maps the batch index to the address of the verifier that was used. The owner of this contract can call the updateVerifier function in order to update the verifier. For this update to succeed, it requires that the provided startBatchIndex is greater than or equal to the previous verifier's startBatchIndex.

However, it does not check if that batch number has already been verified by the current verifier, which could be confusing. For example, if the current verifier's start index is 100, and it has verified batches up to batch 105, the new verifier could be set with a start index of 102. The event emitted would contain the index of 102, which would be confusing because it would appear to a user monitoring the events as though the new verifier was used to verify the batches 102-105 when in reality it was not. This could even be used maliciously by the owner to hide information relating to a faulty verifier.

Consider enforcing that the start index must be greater than the lastFinalizedBatchIndex.

PR title

Your PR title must follow conventional commits (as we are doing squash merge for each PR), so it must start with one of the following types:

• fix: A bug fix

Deployment tag versioning

Has tag in common/version.go been updated?

• No, this PR doesn't involve a new deployment, git tag, docker image tag
• Yes

Breaking change label

Does this PR have the breaking-change label?

• No, this PR is not a breaking change
• Yes

[codecov]

Codecov Report

Merging #849 (6f3f59b) into develop (e08b800) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #849   +/-   ##
========================================
  Coverage    51.28%   51.28%           
========================================
  Files           60       60           
  Lines         5588     5588           
========================================
  Hits          2866     2866           
  Misses        2483     2483           
  Partials       239      239           

Flag	Coverage Δ
bridge	63.51% <ø> (ø)
common	55.43% <ø> (ø)
coordinator	19.15% <ø> (ø)
database	42.85% <ø> (ø)

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[github-actions]

LCOV of commit 6f3f59b during Contracts #1314

Summary coverage rate:
  lines......: 54.1% (972 of 1798 lines)
  functions..: 71.1% (216 of 304 functions)
  branches...: no data found

Files changed coverage rate: n/a