core: Extract pipeline stage methods for process_block

Phase 4 of the runner refactor - Define Pipeline Stages.

This commit extracts the block processing logic into explicit pipeline
stage methods, making process_block much cleaner and easier to follow:

- match_triggers(): Match and decode triggers against hosts
- execute_triggers(): Execute matched triggers via TriggerRunner
- process_dynamic_data_sources(): Handle dynamically created data sources
- process_offchain_triggers(): Process offchain events
- persist_block(): Persist block state to the store

The process_block method now clearly shows the pipeline flow:
Stage 1 -> Stage 2 -> Stage 3 -> Stage 4 -> Stage 5

Author: lutter