Implement the core EV calculation: EV = p*C_success + (1-p)*C_fail
where C_success = scopeCost*impactWeight, C_fail = scopeCost*impactWeight + fallbackCost + timeLost*expectedRetries.
- expectedRetries = (1-p)/p when p>0, else 0 (geometric series)
- Caps expectedRetries at config.retries when retries > 0
- Multiplies final EV by config.valueRate when non-zero
- 30 unit tests covering formula, edge cases, and Python research model values