Don't spawn Anthropic telemetry event when API key is missing

[rtfeldman]

Minor refactor that I'm extracting from a branch because it can stand alone.

• Now we no longer spawn an executor for report_anthropic_event if it's just going to immediately fail due to API key being missing
• report_anthropic_event now takes a String API key instead of Option<String> and the error reporting if the key is missing has been moved to the caller.
• report_anthropic_event is longer coupled to AnthropicError, because all it ever did was generate an AnthropicEvent::Other, which in turn was then only used for log_err - so, can just be an anyhow::Result.

Release Notes:

• N/A