Version 1.0.0-alpha2 - Fix: Consistent scoring behavior in Evaluator and EvaluationSet

Key changes:
- Remove default scores fallback in Evaluator::calculateScore()
- Now returns 0.0 for unknown choices (matching EvaluationSet::getScoreForChoice)
- Update tests to reflect new behavior
- All tests pass (121 unit tests, 131 kernel tests)

This fixes an inconsistency where Evaluator::calculateScore() had a default scores fallback
while EvaluationSet::getScoreForChoice() only returned 0.0 for unknown choices.

Co-authored-by: openhands <openhands@all-hands.dev>