🎯 High Priority: Extract duplicate transaction processing logic

[quantumshiro]

Problem

The execution layer has duplicate transaction processing logic between multiple methods, violating DRY principles and making maintenance difficult.

Specific Duplications Found

File: src/modular/execution.rs

• Lines 283-303: Transaction processing in execute_block method
• Lines 354-368: Similar logic in execute_transaction method
• Pattern: Repeated validation, gas calculation, and state updates

Proposed Refactoring

Create shared helper methods:

impl ExecutionLayer {
    // Extract common transaction processing logic
    fn process_transaction_with_model(&mut self, tx: &Transaction, model: TransactionModel) -> Result<ExecutionResult, ExecutionError>;
    
    // Extract gas calculation logic  
    fn calculate_transaction_gas(&self, tx: &Transaction) -> Result<u64, ExecutionError>;
    
    // Extract state update logic
    fn apply_transaction_state_changes(&mut self, tx: &Transaction, result: &ExecutionResult) -> Result<(), ExecutionError>;
}

Benefits

• ✅ Eliminate code duplication
• ✅ Centralize transaction processing logic
• ✅ Easier to add new transaction types
• ✅ Improved testability
• ✅ Consistent error handling

Definition of Done

• Extract common logic into private methods
• Update execute_block to use shared methods
• Update execute_transaction to use shared methods
• Add unit tests for extracted methods
• Verify all existing tests still pass
• No functional changes to external API

Priority: 🔥 High

This refactoring will make other execution layer improvements much easier.

Estimated Effort: 2-3 days