imatrix: calculate activation-based statistics for new format (GGUF) imatrices (#14891)
* Use activations to calculate the stats
* Determine calculation mode
* Compute entropy for activations
* Compute cosine similarity based on activations
* Compute l2 norm
* Add compute_layer_statistics() function
* Update aggregated statistic report layout
* Fix printing l2 norm when calc_mode = 1
* Refactor variable name
* Compute aggregated (per layer) l2 norm
* Update aggregated sum of squared activations per layer
* Make ZD Score two-tailed
* Update report layout
* Reverse conditional logic to match convention
* Rename report heading
* Add --activation-statistics parameter
* Add Euclidean–Cosine Score (ECS)
* Add --activation-statistics logic to avoid doubling the imatrix size by default
* Update stats output sort based on imatrix type
* Process external NextN draft files (-md / --model-draft)
* Refactor to use new llama_batch_ext
Co-authored-by: compilade <git@compilade.net>
Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@huggingface.co>