feat: added think tool to let agent query a reasoner

[ErikBjare]

TODO

• [ ] Send full conversation context (different mode/tool?)
• [ ] Karpathy-style consortium

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[!IMPORTANT] Adds think tool to enhance reasoning on complex problems using powerful LLMs, with model specification and file content integration.

• New Feature:
  • Adds think tool in gptme/tools/think.py to enhance reasoning on complex problems using more powerful LLMs.
  • Supports specifying a model for reasoning via model parameter.
• Functionality:
  • execute() function processes reasoning requests, reads file contents, and sends them to a specified model.
  • Logs model usage and handles file reading errors.
• Tool Specification:
  • ToolSpec defines tool parameters and usage instructions, including the need to specify files in requests.
• Future Enhancements:
  • TODOs for implementing a consortium approach for aggregating responses from multiple models.

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