[FVM] Integrate scheduled callbacks into block execution workflow

[devbugging]

Summary

Integrate scheduled callback processing into the block execution workflow, enabling automatic callback processing during system transaction execution when callbacks are enabled.

Changes

Modified Files

• engine/execution/computation/computer/computer.go - Main integration logic
• engine/execution/computation/computer/result_collector.go - Result handling updates

Key Features

• executeProcessCallback() - Executes callback processing transaction and extracts ready callbacks
• queueSystemTransaction() - Enhanced to handle callback transactions in system collection
• Automatic callback processing when ScheduleCallbacksEnabled is true
• Proper transaction ordering: process → execute callbacks → system transaction

Technical Implementation

• Callbacks execute as part of system chunk processing
• Process transaction identifies ready callbacks via events
• Individual callback execution transactions generated dynamically
• All transactions properly recorded in system collection for verification

Execution Flow

1. Process Phase: Execute callback processor transaction to identify ready callbacks
2. Execute Phase: Generate and execute individual callback transactions based on events
3. System Phase: Execute standard system chunk transaction

Testing

Testing is a follow-up task that needs to be done after I complete adding core-contract for scheduler contract.

Dependencies

• Requires FVM context infrastructure and callback blueprints from previous PRs
• Adding core-contract for callback scheduler
• Ready for production use when feature flag is enabled
• PR https://github.com/onflow/flow-go/pull/7492
• PR https://github.com/onflow/flow-go/pull/7493