feat(aws): Add Amazon Nova 2.0 support with system tools and reasoning configuration

[dkovvuri]

Add comprehensive support for Amazon Nova 2.0 models including system tools
(nova_grounding and nova_code_interpreter) and reasoning configuration with
string-based validation.

Features:

• Add NovaSystemTool, NovaGroundingTool, and NovaCodeInterpreterTool helpers
• Support system tools via bind_tools() with both helper classes and strings
• Add reasoning configuration validation (accepts "low", "medium", "high")
• Support reasoning in both streaming and non-streaming modes
• Parse Nova's reasoningContent format to standard LangChain content blocks
• Add IAM permission error handling for bedrock:InvokeTool