Include ai_credits_this_response in AI credits usage JSONL parsing

[Copilot]

The AI Credits usage parser was only recognizing existing explicit credit fields and could miss consumption reported as ai_credits_this_response. This update extends explicit credit extraction so usage totals include that field as well.

• Parser field precedence update

  • Extended explicit AI credit aliases in the JSONL helper to include:
    • ai_credits_this_response
    • aiCreditsThisResponse
  • Existing aliases (ai_credits, aiCredits, aic) remain supported.

• Guardrail aggregation alignment

  • The daily guardrail path now correctly counts response-scoped AI credits when present in usage records, avoiding undercounted totals in mixed payload formats.

• Targeted coverage update

  • Added a usage-record case with ai_credits_this_response and updated expected aggregate value accordingly.

const explicitAICredits = getNumericAliasField(usage, parsed, [
  "ai_credits_this_response",
  "aiCreditsThisResponse",
  "ai_credits",
  "aiCredits",
]);