Add client-side timeout and safe comparison for Python challenge runs

[Copilot]

User-submitted Python solutions were able to hang indefinitely despite the intended 5s limit, and incorrect outputs (e.g., None) were not always handled safely. The system should always return the actual output or a timeout error within 5 seconds.

• Timeout enforcement (Python runs): introduce a dedicated Python runner with an AbortController-backed 5s client timeout and shared timeout constants to keep behavior consistent with JS runs.
• Result validation: guard schema-matching comparisons to fail cleanly when outputs are not arrays.

Example:

const RUN_TIMEOUT_MS = 5000
const RUN_TIMEOUT_MESSAGE = 'Timeout (5s)'

async function runPython(harnessTemplate, userCode, input) {
  const controller = new AbortController()
  const timeout = setTimeout(() => controller.abort(), RUN_TIMEOUT_MS)
  // ...
}