Adds a per-layer K/V ring (kv-cache.h) backed by a dedicated backend
buffer, sized at init for max_seq_len positions. The talker holds a
4096 position cache (896 MB f32) for the LM context, the code
predictor a 16 position cache (~80 KB) reset every frame.
talker_forward splits into prefill (resets the cache and writes T
positions in one shot) and decode (appends one position, reads the
[0, cur_len+1) window). code_predictor_step does the same with a T=2
prefill plus 14 single token decodes.
Bit identical audio output, validated by sha256 against the pre KV
cache run on a 64 frame F32 reference seed=42. Walltime drops ~10%
on a single utterance ; the win scales with sequence length and
unlocks frame by frame streaming.
Pascal