Fix for terminal flickering when streaming plans 📺

Improvements to stream handling that greatly reduce flickering in the terminal when streaming a plan, especially when many files are being built simultaneously. CPU usage is also reduced on both the client and server side.

Claude 3.5 Sonnet model pack is now built-in 🧠

You can now easily use Claude 3.5 Sonnet with Plandex through OpenRouter.ai.

1. Create an account at OpenRouter.ai if you don't already have one.
2. Generate an OpenRouter API key.
3. Run export OPENROUTER_API_KEY=... in your terminal.
4. Run plandex set-model, select choose a model pack to change all roles at once and then choose either anthropic-claude-3.5-sonnet (which uses Claude 3.5 Sonnet for all heavy lifting and Claude 3 Haiku for lighter tasks) or anthropic-claude-3.5-sonnet-gpt-4o (which uses Claude 3.5 Sonnet for planning and summarization, gpt-4o for builds, and gpt-3.5-turbo for lighter tasks)

Remember, you can run plandex model-packs for details on all built-in model packs.