Add support for Claude models

[slowpoke111]

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Feature description

Add support for using Anthropic's Claude models. They can be accessed through the anthropic python library and have similar syntax to the openai module.

Motivation/Application

This could allow for more user control over the results as Claude performs better on some tasks.

[chaelli]

imho that already works
try
export ANTHROPIC_API_KEY=......
and then
gpte --model "claude-3-5-sonnet-20241022"