TLS Handshake Timeout and 400 Error Using Context Caching

### Description of the bug:

I'm encountering intermittent errors when using context caching with the gemini-1.5-pro-002 model or another in the generative-ai-go library. The errors include TLS handshake timeouts and API error 400 responses.

Here are some examples of the errors I encountered:

## Code to Reproduce
Here is the relevant part of my implementation:
```go
ctx := context.Background()
argcc := &genai.CachedContent{
Expiration: genai.ExpireTimeOrTTL{
ExpireTime: time.Now().Add(1 * time.Hour),
},
Model: "gemini-1.5-pro-002",
SystemInstruction: genai.NewUserContent(genai.Text("Example system instruction")),
Contents: content, // Multiple PDFs loaded as genai.Content
}

cc, err := g.Client.CreateCachedContent(ctx, argcc)
if err != nil {
fmt.Printf("Error creating cached content: %v", err)
panic(err)
}

resp, err := g.Session.SendMessage(ctx, genai.Text("Example prompt"))
if err != nil {
fmt.Printf("Error sending message: %v", err)
panic(err)
}

```

### Actual vs expected behavior:

I should receive the response

### Any other information you'd like to share?

I'm using the latest version of the SDK.

I've already set my json credentials and Gemini API KEY.