Implement basic contribution scoring logic

[AbdulSnk]

Overview

StreamForge Core needs a scoring module that takes ingested contribution events and produces a deterministic score for each contributor. This score will later feed into the reward calculation pipeline.

What needs to be done

• Create a scoring module under src/
• Implement a score_event function that accepts an Event struct and returns a numeric score
• Apply basic scoring rules:
  • pull_request event = 10 points
  • commit event = 5 points
  • review event = 3 points
  • unknown event types = 0 points
• Implement a aggregate_scores function that takes a list of events and returns total score per contributor

Acceptance Criteria

• src/scoring.rs module exists and is wired into main.rs
• score_event correctly returns points based on event type
• aggregate_scores correctly totals scores per contributor
• Unit tests cover all event types including unknown types
• Edge cases handled: empty list, single event, multiple contributors

Pre-Submission Checklist

• I have run cargo build locally and it succeeds
• I have run cargo test locally and all tests pass
• I have run cargo fmt to format my code
• I have run cargo clippy and fixed all warnings

Notes

Scoring rules are intentionally simple for now. The goal is a clean, testable foundation that can be extended later with weighted scoring.