Fix native library loader silently failing when CUDA DLLs are missing

Change all 'ok = TryLoadNativeLibraryByName(...)' calls to 'ok &= ...' so that
failures accumulate instead of being overwritten by subsequent successful loads.
Initialize 'ok = true' before the loading chain.

Previously, each load call overwrote the result of the previous one, so if an
early CUDA dependency (e.g. cudnn_adv64_9) failed to load but LibTorchSharp
succeeded, 'ok' would be true. This caused:
- nativeBackendCudaLoaded set to true despite missing dependencies
- The fallback loading path was skipped
- The diagnostic trace (StringBuilder) was discarded
- Subsequent load attempts were skipped entirely
- CUDA operations failed later with cryptic errors

Now any single load failure keeps 'ok' as false, ensuring the fallback path is
attempted and the full diagnostic trace is preserved in error messages.

Fixes #1545

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: alinpahontu2912

src/TorchSharp/Torch.cs

@@ -116,7 +116,7 @@ private static void LoadNativeBackend(bool useCudaBackend, out StringBuilder? tr
             trace = null;
 
             if (!alreadyLoaded) {
-                bool ok;
+                bool ok = true;
                 trace = new StringBuilder();
                 trace.AppendLine($"");
                 trace.AppendLine($"TorchSharp: LoadNativeBackend: Initialising native backend, useCudaBackend = {useCudaBackend}");
@@ -134,27 +134,27 @@ private static void LoadNativeBackend(bool useCudaBackend, out StringBuilder? tr
                         // Preloading these DLLs on windows seems to iron out problems where one native DLL
                         // requests a load of another through dynamic linking techniques.
                         //
-                        ok = TryLoadNativeLibraryByName("cudnn_adv64_9", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cudnn_cnn64_9", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cudnn_ops64_9", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cudnn_graph64_9.dll", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cudnn_heuristic64_9.dll", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cudnn_engines_precompiled64_9.dll", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cudnn_engines_runtime_compiled64_9.dll", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("nvrtc-builtins64_128", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("caffe2_nvrtc", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("nvrtc64_120_0", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cublasLt64_12", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cufft64_11", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cusparse64_12", typeof(torch).Assembly, trace);
-                        ok = TryLoadNativeLibraryByName("cusolver64_11", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_adv64_9", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_cnn64_9", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_ops64_9", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_graph64_9.dll", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_heuristic64_9.dll", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_engines_precompiled64_9.dll", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cudnn_engines_runtime_compiled64_9.dll", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("nvrtc-builtins64_128", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("caffe2_nvrtc", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("nvrtc64_120_0", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cublasLt64_12", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cufft64_11", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cusparse64_12", typeof(torch).Assembly, trace);
+                        ok &= TryLoadNativeLibraryByName("cusolver64_11", typeof(torch).Assembly, trace);
                     }
 
-                    ok = TryLoadNativeLibraryByName("torch_cuda", typeof(torch).Assembly, trace);
-                    ok = TryLoadNativeLibraryByName("LibTorchSharp", typeof(torch).Assembly, trace);
+                    ok &= TryLoadNativeLibraryByName("torch_cuda", typeof(torch).Assembly, trace);
+                    ok &= TryLoadNativeLibraryByName("LibTorchSharp", typeof(torch).Assembly, trace);
                 } else {
-                    ok = TryLoadNativeLibraryByName("torch_cpu", typeof(torch).Assembly, trace);
-                    ok = TryLoadNativeLibraryByName("LibTorchSharp", typeof(torch).Assembly, trace);
+                    ok &= TryLoadNativeLibraryByName("torch_cpu", typeof(torch).Assembly, trace);
+                    ok &= TryLoadNativeLibraryByName("LibTorchSharp", typeof(torch).Assembly, trace);
                 }
 
                 trace.AppendLine($"    Result from regular native load of LibTorchSharp is {ok}");