providerFor function
Builds the AiProvider matching config's provider kind, sharing client
for all requests.
Implementation
AiProvider providerFor(AiConfig config, http.Client client) =>
switch (config.provider) {
AiProviderKind.anthropic => AnthropicProvider(config, client),
AiProviderKind.openai => OpenAiProvider(config, client),
AiProviderKind.gemini => GeminiProvider(config, client),
};