llama : add llama_model_ftype_name() (#25134)

* llama : add llama_model_ftype_name()

Expose the model file type (quantization) name, e.g. "Q8_0" or
"Q4_K - Medium", through a new public C API. The returned pointer is
valid for the lifetime of the model and nullptr when the model is
invalid or the file type is unknown.

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* Export enum

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* s/llama_model_ftype_name/llama_ftype_name/

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* Move "(guessed)" to the front in llama_ftype_name

Prepend the "(guessed)" label instead of appending it. This allows removing
the non-thread-safe static std::string, making the function allocation-free.

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* Add LLAMA_FTYPE_PREFIX

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

* Dont check for model

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

---------

Signed-off-by: Adrien Gallouët <angt@huggingface.co>

src/llama-model.cpp

@@ -987,6 +987,8 @@ struct llama_model::impl {
 
     std::string desc_str;
 
+    llama_ftype ftype = LLAMA_FTYPE_ALL_F32;
+
     // model memory mapped files
     llama_mmaps mappings;
 
@@ -1200,6 +1202,8 @@ void llama_model_base::load_hparams(llama_model_loader & ml) {
 
     pimpl->desc_str = arch_name() + " " + type_name() + " " + ml.ftype_name();
 
+    pimpl->ftype = ml.ftype;
+
     if (hparams.f_max_alibi_bias > 0.0f) {
         hparams.use_alibi = true;
     }
@@ -1646,6 +1650,10 @@ std::string llama_model::desc() const {
     return pimpl->desc_str;
 }
 
+llama_ftype llama_model::ftype() const {
+    return pimpl->ftype;
+}
+
 size_t llama_model::size() const {
     return pimpl->n_bytes;
 }
@@ -2616,6 +2624,10 @@ int32_t llama_model_desc(const llama_model * model, char * buf, size_t buf_size)
     return snprintf(buf, buf_size, "%s", model->desc().c_str());
 }
 
+llama_ftype llama_model_ftype(const llama_model * model) {
+    return model->ftype();
+}
+
 uint64_t llama_model_size(const llama_model * model) {
     return model->size();
 }