Refactor(consensus): split oversized process function and eliminate panic risks in main loop

[raushan728]

Description

Refactored massa-consensus-worker to improve maintainability and reliability:

• Refactoring: Split the oversized ConsensusState::process function into modular helper methods to comply with the 50-line limit (CONTRIBUTING.md).
• Stability: Replaced .expect() and .unwrap() calls in process.rs and main_loop.rs with proper Result propagation and error logging to prevent worker panics.
• Testing: Added unit and integration tests in src/tests/process_refactor.rs to verify state transitions in the refactored logic.

Checklist

• document all added functions
• try in sandbox /simulation/labnet
• if part of node-launch, checked using the resync_check flag
• unit tests on the added/changed features
• make tests compile
• make tests pass
• add logs allowing easy debugging in case the changes caused problems
• if the API has changed, update the API specification