mlx: try loading library via rpath before searching directories (#14322)

The existing code manually searches directories for libmlxc.* and passes
full paths to dlopen, bypassing the binary's rpath. This means MLX
libraries installed via package managers (e.g., Homebrew) aren't found
even when rpath is correctly set at link time.

This change adds a fallback that tries loading via rpath first (using
just the library name), before falling back to the existing directory
search. This follows standard Unix/macOS conventions and works with any
installation that sets rpath.

Fixes library loading on macOS with Homebrew-installed mlx-c without
requiring OLLAMA_LIBRARY_PATH environment variable.

Co-authored-by: Natl <nat@MacBook-Pro.local>

x/mlxrunner/mlx/dynamic.go

@@ -55,6 +55,30 @@ func tryLoadFromDir(dir string) bool {
 	return false
 }
 
+// tryLoadByName attempts to load the library using just its name,
+// allowing the system to use rpath, LD_LIBRARY_PATH, or standard search paths.
+// Returns true if the library was successfully loaded.
+func tryLoadByName() bool {
+	libraryName := "libmlxc.dylib"
+	if runtime.GOOS == "linux" {
+		libraryName = "libmlxc.so"
+	}
+
+	cPath := C.CString(libraryName)
+	defer C.free(unsafe.Pointer(cPath))
+
+	var handle C.mlx_dynamic_handle
+	if C.mlx_dynamic_load(&handle, cPath) != 0 {
+		return false
+	}
+	if C.mlx_dynamic_load_symbols(handle) != 0 {
+		C.mlx_dynamic_unload(&handle)
+		return false
+	}
+
+	return true
+}
+
 func init() {
 	switch runtime.GOOS {
 	case "darwin":
@@ -73,6 +97,11 @@ func init() {
 		}
 	}
 
+	// Try loading via rpath/standard library search
+	if tryLoadByName() {
+		return
+	}
+
 	// Build search paths: executable directory, then build directories
 	var searchDirs []string
 	if exe, err := os.Executable(); err == nil {