refactor: handle GGML_VK_VISIBLE_DEVICES at the Python level (#2179)

All C++ handling code currently:
- build a comma-separated list from the info_vulkan array
- if GGML_VK_VISIBLE_DEVICES isn't set
  - set GGML_VK_VISIBLE_DEVICES to the list

Once set, GGML_VK_VISIBLE_DEVICES affects the whole process. So this
can be done in the same way at the Python level, before all loading
functions.

Caveat: load_model had the default `inputs.vulkan_info = "0"`,
so the default GPU would be "0" only when loading a text model.

otherarch/embeddings_adapter.cpp

@@ -22,7 +22,6 @@
 #endif
 
 static llama_context * embeddings_ctx = nullptr; //text to codes ctx
-static std::string ttsvulkandeviceenv;
 bool embeddings_debug = false;
 static int max_batchsize = 512;
 static std::string last_output = "";
@@ -82,27 +81,12 @@ static void batch_decode(llama_context * ctx, llama_batch & batch, float * outpu
 
 bool embeddingstype_load_model(const embeddings_load_model_inputs inputs)
 {
-    //duplicated from expose.cpp
-    std::string vulkan_info_raw = inputs.vulkan_info;
-    std::string vulkan_info_str = "";
-    for (size_t i = 0; i < vulkan_info_raw.length(); ++i) {
-        vulkan_info_str += vulkan_info_raw[i];
-        if (i < vulkan_info_raw.length() - 1) {
-            vulkan_info_str += ",";
-        }
-    }
-    const char* existingenv = getenv("GGML_VK_VISIBLE_DEVICES");
     std::vector<ggml_backend_dev_t> devices_override;
     std::string dev_override_str = inputs.devices_override;
     if(dev_override_str!="")
     {
         devices_override = kcpp_parse_device_list(dev_override_str);
     }
-    if(!existingenv && vulkan_info_str!="")
-    {
-        ttsvulkandeviceenv = "GGML_VK_VISIBLE_DEVICES="+vulkan_info_str;
-        putenv((char*)ttsvulkandeviceenv.c_str());
-    }
 
     llama_backend_init();