convert: qwen2 from safetensors (#8408)

Add native support for converting Qwen2 family models (including Qwen2.5)
from safetensors to gguf format so we can run it.

convert/convert_test.go

@@ -108,6 +108,7 @@ func TestConvertModel(t *testing.T) {
 		"Phi-3-mini-128k-instruct",
 		"all-MiniLM-L6-v2",
 		"gemma-2-9b-it",
+		"Qwen2.5-0.5B-Instruct",
 	}
 
 	for i := range cases {