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>

include/llama.h

@@ -159,6 +159,9 @@ extern "C" {
         LLAMA_FTYPE_GUESSED = 1024, // not specified in the model file
     };
 
+    // Get the model file type (quantization) as a string, e.g. "Q8_0" or "Q4_K - Medium"
+    LLAMA_API const char * llama_ftype_name(enum llama_ftype ftype);
+
     enum llama_rope_scaling_type {
         LLAMA_ROPE_SCALING_TYPE_UNSPECIFIED = -1,
         LLAMA_ROPE_SCALING_TYPE_NONE        = 0,
@@ -606,6 +609,9 @@ extern "C" {
     // Get a string describing the model type
     LLAMA_API int32_t llama_model_desc(const struct llama_model * model, char * buf, size_t buf_size);
 
+    // Get the model file type (quantization), e.g. LLAMA_FTYPE_MOSTLY_Q8_0
+    LLAMA_API enum llama_ftype llama_model_ftype(const struct llama_model * model);
+
     // Returns the total size of all the tensors in the model in bytes
     LLAMA_API uint64_t llama_model_size(const struct llama_model * model);