google_generative_ai version 0.4.1

• Concatenate multiple TextPart into the text String in case the model
  replies with more than one part.
• Fix handling of format argument to Schema.number and Schema.integer.
• Export UsageMetadata.
• Include the full GenerateContentRequest (previously omitted
  safetySettings, generationConfig, tools, toolConfig, and
  systemInstruction) in countTokens requests. This aligns the token count
  with the token count the backend will see in practice for a
  generateContent request.
• Add a text getter on Candidate to make it easer to retrieve the text from
  candidates other than the first in a response.