server : improve mtmd ctx checkpoints

[ggerganov]

fix #20720
cont #20232

• Fix logic for end-of-prompt-checkpoints in the presence of mtmd chunks
• Checkpoint spacing is now based on number of tokens, not on positions
• Fix off-by-one in pos_min_thold logic

[obn777]

просто , пусть не по теме, делюсь результатом:
{
"timestamp": "12:02:34",
"cpu_load": 0.5,
"ram_load": 32.0,
"gpu_temp": 38,
"gpu_load": 0,
"vram_mb": 4207,
"vector_integrity": 1.0,
"entropy": 0.0,
"status": "STABLE"
}
я перевел на нейронку nitro v 15