MLX - dynamic loading of mlx-c (#13735)

* MLX - dynamic loading of mlx-c

Create a wrapper layer to indirect the dependency on mlx-c so
the main ollama binary does not have a load-time dependency on mlx-c, mlx, and on linux, cuda.  Lazy load the library via dlopen
so we can adjust the path to ensure the dependencies are found
and fail gracefully if not present.

* review comments

* fix broken tests

x/ml/backend/mlx/mlx_dynamic.c

@@ -0,0 +1,92 @@
+// mlx_dynamic.c - Dynamic loading wrapper for MLX-C library
+// This file provides runtime dynamic loading of libmlxc instead of link-time binding
+
+#include "mlx_dynamic.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+#include <windows.h>
+typedef HMODULE lib_handle_t;
+#define LOAD_LIB(path) LoadLibraryA(path)
+#define GET_SYMBOL(handle, name) GetProcAddress(handle, name)
+#define CLOSE_LIB(handle) FreeLibrary(handle)
+#define LIB_ERROR() "LoadLibrary failed"
+static const char* LIB_NAMES[] = {"libmlxc.dll", NULL};
+#else
+#include <dlfcn.h>
+typedef void* lib_handle_t;
+#define LOAD_LIB(path) dlopen(path, RTLD_LAZY | RTLD_GLOBAL)
+#define GET_SYMBOL(handle, name) dlsym(handle, name)
+#define CLOSE_LIB(handle) dlclose(handle)
+#define LIB_ERROR() dlerror()
+#ifdef __APPLE__
+static const char* LIB_NAMES[] = {
+    "libmlxc.dylib",
+    "@loader_path/../build/lib/ollama/libmlxc.dylib",
+    "@executable_path/../build/lib/ollama/libmlxc.dylib",
+    "build/lib/ollama/libmlxc.dylib",
+    "../build/lib/ollama/libmlxc.dylib",
+    NULL
+};
+#else
+static const char* LIB_NAMES[] = {
+    "libmlxc.so",
+    "$ORIGIN/../build/lib/ollama/libmlxc.so",
+    "build/lib/ollama/libmlxc.so",
+    "../build/lib/ollama/libmlxc.so",
+    NULL
+};
+#endif
+#endif
+
+static lib_handle_t mlx_handle = NULL;
+static int mlx_initialized = 0;
+static char mlx_error_buffer[512] = {0};
+
+// Initialize MLX dynamic library
+// Returns 0 on success, -1 on failure
+// On failure, call mlx_dynamic_error() to get error message
+int mlx_dynamic_init(void) {
+    if (mlx_initialized) {
+        return 0;  // Already initialized
+    }
+
+    // Try each possible library path
+    for (int i = 0; LIB_NAMES[i] != NULL; i++) {
+        mlx_handle = LOAD_LIB(LIB_NAMES[i]);
+        if (mlx_handle != NULL) {
+            mlx_initialized = 1;
+            snprintf(mlx_error_buffer, sizeof(mlx_error_buffer),
+                     "MLX: Successfully loaded %s", LIB_NAMES[i]);
+            return 0;
+        }
+    }
+
+    // Failed to load library
+    const char* err = LIB_ERROR();
+    snprintf(mlx_error_buffer, sizeof(mlx_error_buffer),
+             "MLX: Failed to load libmlxc library. %s",
+             err ? err : "Unknown error");
+    return -1;
+}
+
+// Get the last error message
+const char* mlx_dynamic_error(void) {
+    return mlx_error_buffer;
+}
+
+// Check if MLX is initialized
+int mlx_dynamic_is_initialized(void) {
+    return mlx_initialized;
+}
+
+// Cleanup (optional, called at program exit)
+void mlx_dynamic_cleanup(void) {
+    if (mlx_handle != NULL) {
+        CLOSE_LIB(mlx_handle);
+        mlx_handle = NULL;
+        mlx_initialized = 0;
+    }
+}