feat: piggybacking OpenAI endpoints

[erhant]

NOTE: this is just food for thought, it's kind of a non-trivial feature from the user's perspective.

OpenAI has the v1/models/* endpoints, see here. We might make use of these as follows (also serves for the purpose of OpenAI compat #3)

• GET /v1/models/list lists the supported models
• GET /v1/models/{model} prepares the topology for the given model, akin to calling prepare_topology
  • we would need some extra request parameters (such as strategy, but we could embed them into the {model} param too, e.g. ring:gpt-oss-20b); bit smelly though
• DELETE /v1/models/ unloads the model, akin to calling unload_model on API.

The idea here is to allow the entire user-flow of dnet to be achievable with openai compatibility, which enables us to use all existing OpenAI-compatible clients out there.