Use Markov Chain for temporal prediction

[supastishn]

This uses a Markov chain to assist with prediction of experts which should achieve higher accuracy.

[Helldez]

Sorry for the wait. Before I can judge this I need a number, not a description:

• Run --predict-log on a real model with and without the chain and post both. It reports predictor accuracy per layer, it exists for exactly this.
• clang-format 18 on the touched files (CI checks it), and please keep the comments you removed in session.cpp.

One thing to know going in: I re-measured prefetch on the phone today and it loses even when the prediction is right (+44% bytes for -14% stall, tok/s down). Better prediction helps only if it costs fewer bytes.