model : add reasoning/tool parsing to Llama 3.x Nemotron

[aldehir]

This PR adds reasoning and tool parsing to the Llama 3.x Nemotron models.

Context:

• The generic parser excludes the <think></think> tags, and I believe the sampling is also inhibiting the model from reasoning.
• The think tags are not unique tokens, so it outputs tokens <think when streaming until the reasoning parsing has enough to match.

Implementation:

• Added COMMON_CHAT_FORMAT_LLAMA_3_X_NEMOTRON and associated init/parse functions.
• Added try_consume_partial_literal() to defer parsing when there's a prefix match, but I don't know if that's the best way. Could be named better too.