Parse transcript prioritization booleans explicitly

[YT-er]

Summary

• replace eval() in transcript prioritization with explicit boolean parsing
• accept booleans plus the existing True, False, and Not Run string values
• reject unexpected values with a contextual error
• add regression coverage for valid, invalid, and malicious inputs

Why

Transcript fields may originate in parsed tabular data. Evaluating their contents as Python can execute unintended code and treats malformed input unpredictably.

Impact

Existing supported values preserve their behavior. Unexpected values now fail deterministically instead of being evaluated.

Validation

• python -m unittest tests.test_run_utils — 4 tests passed
• Python compile check passed for the changed source and test
• git diff --check passed

This is one focused replacement for part of #1430 and is based on 8.0.0.

AI assistance disclosure

This PR was AI-assisted using OpenAI Codex for implementation, test drafting, and command execution. I reviewed the diff line by line, ran the validation above, and take responsibility for the submitted changes.