aiRequestMs function
The request duration to record for a provider call: the Hub-reported upstream
time from kAiProxyElapsedMsHeader when present (proxied requests), otherwise
the locally measured localMs.
Implementation
int aiRequestMs(Map<String, String> headers, int localMs) {
final raw = headers[kAiProxyElapsedMsHeader];
final reported = raw == null ? null : int.tryParse(raw.trim());
return (reported != null && reported >= 0) ? reported : localMs;
}