Chore sequencer plugin core readability

[fluentcrafter]

This PR implements issue(s) #

Checklist

• I wrote new tests for my new core changes.
• I have successfully ran tests, style checker and build against my new changes locally.
• I have informed the team of any breaking changes if there are any.

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Note

Refactors liveness bundle selection in LineaTransactionSelectorFactory to early-return on missing/empty services, streamline evaluation, and centralize uptime metric updates with commit/rollback.

• Sequencer – Transaction Selection:
  • Streamlines checkAndSendLivenessBundle in LineaTransactionSelectorFactory:
    • Early-return if livenessService is absent or no liveness bundle is built.
    • Replaces nested Optional usage with direct local reference to livenessService.
    • Consolidates evaluation flow: logs, detects interrupt, updates uptime metrics, and commits/rolls back accordingly.
    • Uses livenessService.updateUptimeMetrics(...) consistently after success/failure.

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