UI updates

• Optimize the UI: events triggered by clicking on buttons, selecting values from dropdown menus, etc have been refactored to minimize the number of connections made between the UI and the server. As a result, the UI is now significantly faster and more responsive.
• Use chat-instruct mode by default: most models nowadays are instruction-following models, and this mode automatically uses the model's Jinja2 template to generate the prompt, leading to higher-quality outputs.
• Improve the style of code blocks in light mode.
• Increase the font weight of chat messages (for chat and chat-instruct modes).
• Use gr.Number for RoPE scaling parameters (#6233). Thanks @Vhallo.
• Don't export the instruction template to settings.yaml on "Save UI defaults to settings.yaml" (it gets ignored and replaced with the model template).

Backend updates

• llama-cpp-python: bump to 0.2.83 (adds Mistral-Nemo support).

Other changes

• training: Added ChatML-format.json format example (#5899). Thanks @FartyPants.
• Customize the subpath for gradio, use with reverse proxy (#5106). Thanks @canoalberto.

Bug fixes

• Fix an issue where the chat contents sometimes disappear for a split second during streaming (#6247). Thanks @Patronics.
• Fix the chat UI losing its vertical scrolling position when the input area grows to more than 1 line.