fix: improve performance of ApplyPowerTableDiffs in ImportSnapshotToDatastore

[hanabi1224]

The sort operation in ApplyPowerTableDiffs turns out to be expensive.
This PR introduces another func ApplyPowerTableDiffsToMap(powerTableMap map[gpbft.ActorID]gpbft.PowerEntry, diffs ...PowerTableDiff) (map[gpbft.ActorID]gpbft.PowerEntry, error) to avoid sorting.

It also adds more validations against first instance, latest instance and powertable cid.

Perf stats of importing a mainnet F3 snapshot on my laptop show ~99% perf gain

# PR
0.884s
0.773s
0.864s

# main
86.547s
88.422s
86.998s

[codecov]

Codecov Report

❌ Patch coverage is 53.96825% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.38%. Comparing base (9288fba) to head (c04cb35).

Files with missing lines	Patch %	Lines
certstore/snapshot.go	30.95%	18 Missing and 11 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1047      +/-   ##
==========================================
- Coverage   64.77%   64.38%   -0.40%     
==========================================
  Files          81       81              
  Lines        9896     9942      +46     
==========================================
- Hits         6410     6401       -9     
- Misses       2961     3005      +44     
- Partials      525      536      +11     

Files with missing lines	Coverage Δ
certs/certs.go	94.28% <100.00%> (+0.34%)	⬆️
certstore/snapshot.go	41.61% <30.95%> (-6.22%)	⬇️

... and 5 files with indirect coverage changes

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[Copilot]

Pull Request Overview

This PR optimizes the performance of applying power table diffs during F3 snapshot import by introducing a new map-based approach that avoids expensive sorting operations on each iteration. The optimization shows a ~99% performance improvement when importing mainnet F3 snapshots.

• Introduced ApplyPowerTableDiffsToMap function to work with power table maps instead of sorted arrays
• Added comprehensive validation for instance numbers, latest instance bounds, and power table CID verification
• Refactored importSnapshotToDatastoreWithTestingPowerTableFrequency to use the new map-based approach and include additional safety checks

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
certstore/snapshot.go	Refactored snapshot import logic to use map-based power table operations and added validation checks
certs/certs.go	Added new map-based power table diff functions and helper functions for array-map conversion

[Copilot]

The function writes header.LatestInstance but should write the actual latest processed instance. If the loop breaks early due to EOF, this could write an incorrect latest instance number.

Suggested change

	return cs.writeInstanceNumber(ctx, certStoreLatestKey, header.LatestInstance)
	return cs.writeInstanceNumber(ctx, certStoreLatestKey, latestProcessedInstance)

[Kubuxu]

This also seems valid.
Alternative is erroring out if header.Latest is different from latestCert.GPBFTInstance

[hanabi1224]

Fixed by returning err when latestCert.GPBFTInstance != header.LatestInstance

[Copilot]

Potential nil pointer dereference if no certificates are processed (empty snapshot). latestCert will be nil if the loop never executes due to immediate EOF.

Suggested change

	pt := certs.PowerTableMapToArray(ptm)
	pt := certs.PowerTableMapToArray(ptm)
	if latestCert == nil {
	return ErrUnknownLatestCertificate
	}

[Kubuxu]

This seems to be a valid issue. The suggested resolution could be better.

[hanabi1224]

Fixed by adding nil check

[Kubuxu]

SGTM apart from the two issues highlighted by Copilot