fix: ensure Nova models start with user message in chat

[sginji]

• Added _is_nova_model method to detect Nova models
• Updated _format_messages_for_provider to ensure conversations start with user message
• Added unit tests for Nova model detection and message formatting
• Fixes [BUG] CrewAI Chat - Amazon Nova models not supported #3298

Before the fix

crewai chat

Starting a conversation with the Crew
Type 'exit' or Ctrl+C to quit.


Analyzing crew and required inputs - this may take 3 to 30 seconds depending on the complexity of your crew.
..╭───────────────────────────────────────────────────── LLM Error ──────────────────────────────────────────────────────╮
│                                                                                                                      │
│  ❌ LLM Call Failed                                                                                                  │
│  Error: litellm.BadRequestError: Invalid Message bedrock requires at least one non-system message                    │
│                                                                                                                      │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯

After the fix

$ crewai chat

Starting a conversation with the Crew
Type 'exit' or Ctrl+C to quit.


Analyzing crew and required inputs - this may take 3 to 30 seconds depending on the complexity of your crew.
....

Finished analyzing crew.

Assistant: Hey! I'm here to help you with uncovering and reporting cutting-edge developments through thorough research and detailed analysis. Could you please provide me with a topic you're interested in? This will help us generate a comprehensive research report and detailed analysis.

For example, you can specify a topic like "artificial intelligence," "renewable energy," or "quantum computing." Once you provide the topic, please also specify the current year for the research data.

Looking forward to diving into your chosen topic!


You (type your message below. Press 'Enter' twice when you're done):
give me the latest findings on dog obedience training in 2025

....
....

## Conclusion
The field of dog obedience training in 2025 is marked by significant advancements and a deeper understanding of canine behavior and cognition. From positive reinforcement techniques and technology integration to customizable training plans and holistic approaches, the modern training landscape offers a variety of tools and methods to support effective and compassionate training. As the industry continues to evolve, ongoing research and innovation will further enhance the ways in which we train and care for our canine companions.


You (type your message below. Press 'Enter' twice when you're done):
✅ Crew: crew
├── 📋 Task: f2b8077a-38ab-4017-8330-7b8e28c2c659
│   Assigned to: dog obedience training Senior Data Researcher
│   
│   Status: ✅ Completed
├── 📋 Task: 9e1f84d4-2c0c-4071-b428-331e6814e8e3
│   Assigned to: dog obedience training Reporting Analyst
│   
│   Status: ✅ Completed
├── 🔧 Using NovaChatTest from LLM available_function
└── ✅ Tool Usage Completed

[lucasgomide]

@sginji would you mind to fix linter and sync your branch?

[sginji]

@sginji would you mind to fix linter and sync your branch?

thanks for the review! will do 👍🏽

[sginji]

@sginji would you mind to fix linter and sync your branch?

I've pushed lint fixes and rebased my branch. Mind taking another look?