Fail fast when Alpha Vantage refuses a request for the account

[werwolfby]

Problem

On a free Alpha Vantage key, GetRecordsAsync gets this reply every time:

{
  "Information": "Thank you for using Alpha Vantage! This is a premium endpoint. You may subscribe to any of the premium plans at https://www.alphavantage.co/premium/ to instantly unlock all premium endpoints"
}

It arrives with HTTP 200, so the parser read it as invalid data ("data is invalid"). The retry policy then ran through the whole back-off budget, even though retrying can never change this answer.

Changes

• New public FinanceNetAccessDeniedException : FinanceNetException, thrown when the provider refuses the request for the account. Existing catch (FinanceNetException) handlers keep working.
• AlphaVantageService.ThrowIfRejected checks every response from all four methods. It throws the new exception for a premium-endpoint reply or an invalid/missing API key.
• PollyPolicyFactory does not retry the new exception, and the service does not wrap it (InnerException is null), the same as FinanceNetNoDataException.
• The invalid-API-key check used to be only in GetForexRecordsAsync, where it was retried. It now covers all methods and fails at once.
• The rate-limit reply ("higher API call volume") is still retried, because the per-minute limit clears on its own.
• GetRecordsAsync still calls TIME_SERIES_DAILY_ADJUSTED, for backward compatibility. On a free key it now fails at once with a clear message instead of retrying.

Tests

• New AlphaVantageRejectedRequestTests sends the premium reply and the invalid-key reply to each of the four methods and checks that exactly one request is made. It also checks that the rate-limit reply is still retried.
• Against the old code, all 8 refusal cases fail; with the change they pass.
• dotnet test --filter TestCategory=Unit: 204 passed.
• Release build: 0 warnings.

Adding a public exception type calls for a minor version bump in the next release.

[thorstenalpers]

Thanks, great diagnosis. I reproduced it: the same call takes about 6 minutes on main and fails in under a second with your change. Merging. I'll follow up with a small fix for the negative cases in the Alpha Vantage integration tests, they use Assert.ThrowsAsync with the exact base type and need CatchAsync now. Nothing you need to do.