[WIP] Add model IDs for Claude Sonnet and Haiku

[Copilot]

Plan to add new Claude 4.5 model IDs:

• Add Claude 4.5 Haiku to AnthropicModels.cs (claude-haiku-4-5-20251001)
• Fix VertexAI Claude 4.5 Sonnet model ID (corrected to claude-sonnet-4-5@20250929)
• Fix VertexAI Claude 4 Opus model ID (corrected to claude-opus-4@20250514)
• Add Claude 4.5 Haiku to VertexAIModels.cs (claude-haiku-4-5@20251001)
• Add documentation comments about extended thinking support for new models
• Build and verify changes

Changes made:

• Added Claude45Haiku constant to AnthropicModels.cs with model ID "claude-haiku-4-5-20251001"
• Added Claude45Haiku constant to VertexAIModels.cs with model ID "claude-haiku-4-5@20251001"
• Updated Claude45Sonnet in VertexAIModels.cs to correct model ID "claude-sonnet-4-5@20250929"
• Fixed Claude4Opus in VertexAIModels.cs to correct model ID "claude-opus-4@20250514"
• Added "Supports extended thinking" documentation to both new models
• All changes build successfully with no errors

Original prompt

Please add the follow model ids:

claude-sonnet-4-5-20250929 (VertexAI: claude-sonnet-4-5@20250929)
claude-haiku-4-5-20251001 (VertexAI: claude-haiku-4-5@20251001)

Both support extended thinking.
Max output is 64K tokens for both.
Max input is 200K tokens for both, but sonnet-4-5 can go up to 1M (with the right beta header, cannot recall if it's supported by C# SDK yet - it is context-1m-2025-08-07)

Refer to: https://docs.claude.com/en/docs/about-claude/models/overview
For further details and updated informal model descriptions

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