refactor cross-header settlement checks to use a unified function

[AdoAdoAdo]

Reasoning behind the pull request

Proposed changes

Testing procedure

Pre-requisites

Based on the Contributing Guidelines the PR author and the reviewers must check the following requirements are met:

• was the PR targeted to the correct branch?
• if this is a larger feature that probably needs more than one PR, is there a feat branch created?
• if this is a feat branch merging, do all satellite projects have a proper tag inside go.mod?

[Copilot]

Pull request overview

Refactors cross-header settlement gating to consistently honor epoch and round activation.

Changes:

• Adds a shared settlement activation helper.
• Applies round-aware gating across tracking and block-processing paths.
• Expands activation tests and updates shard ID parsing.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Summary
testscommon/enableRoundsHandlerStub.go	Adds configurable round handler test stub.
process/track/crossHeaderSettlement_test.go	Updates settlement test fixtures.
process/track/contendedHeadersProofPuller.go	Filters inactive settlement candidates.
process/track/contendedHeadersProofPuller_test.go	Tests round activation filtering.
process/track/blockProcessor.go	Applies unified gating; critical nil round-handler validation issue remains.
process/track/blockProcessor_test.go	Adds activation-state coverage.
process/block/shardblockProposal_test.go	Updates shard proposal tests.
process/block/shardblock_test.go	Adds round activation coverage.
process/block/metablockProposal.go	Applies gating during proposal selection.
process/block/metablockProposal_test.go	Expands proposal-path coverage.
process/block/metablock_test.go	Adds round activation scenarios.
process/block/baseProcess.go	Uses unified settlement gating.
epochStart/bootstrap/fromLocalStorage.go	Parses shard IDs as unsigned values.
common/common.go	Adds unified gating; nil round-handler handling can cause a panic.
common/common_test.go	Tests activation combinations.

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[codecov]

Codecov Report

❌ Patch coverage is 94.20290% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.71%. Comparing base (707263a) to head (a599f7b).

Files with missing lines	Patch %	Lines
process/track/contendedHeadersProofPuller.go	20.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##           rc/supernova    #7971   +/-   ##
=============================================
  Coverage         77.70%   77.71%           
=============================================
  Files               893      893           
  Lines            129697   129731   +34     
=============================================
+ Hits             100784   100815   +31     
  Misses            22325    22325           
- Partials           6588     6591    +3     

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