cli: new CLI experience

[ngxson]

Ref: #17618

Fix: #11202

We are moving to a new CLI experience with the main code built on top of llama-server. This brings many additional features into llama-cli, making the experience feels mostly like a smaller version of the web UI:

• Multimodal support
• Regenerate last message
• Speculative decoding
• Fully jinja support (including some edge cases that old llama-cli doesn't support)

TODO:

• Use reasoning_content when possible, depends on server: delegate result_state creation to server_task #17835
• Allow using left/right arrow to edit current message, depends on Feature request: add support for left/right arrow for console::readline #17828
• Maybe allow up/down arrow for history (not sure), depends on Feature request: add support for up/down history in console::readline #17829
• Allow reporting timings
• Show progress if prompt processing takes too long quite complicated, do it later
• Support --image and --audio arguments
• Add messages to warn user to move to llama-completion for legacy features