fix: CMake Vulkan/ROCm graceful fallback + GoogleTest timestamp warning

Fixes #2: "Manually-specified variables were not used by the project: TQ_BUILD_VULKAN"

- Vulkan/ROCm: change find_package from REQUIRED to QUIET with
  graceful fallback — prints helpful warning instead of hard error
  when SDK is not installed
- GoogleTest: add DOWNLOAD_EXTRACT_TIMESTAMP TRUE to suppress
  CMP0135 policy warning on newer CMake versions

32/32 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: unamedkr

CMakeLists.txt

@@ -145,30 +145,42 @@ if(TQ_BUILD_CUDA)
     message(STATUS "TurboQuant: CUDA backend enabled")
 endif()
 
-# Vulkan backend (cross-platform GPU)
+# Vulkan backend (cross-platform GPU — AMD, NVIDIA, Intel)
 if(TQ_BUILD_VULKAN)
-    find_package(Vulkan REQUIRED)
-    file(GLOB TQ_VULKAN_SOURCES src/backend/vulkan/*.c)
-    target_sources(turboquant PRIVATE ${TQ_VULKAN_SOURCES})
-    target_sources(turboquant_shared PRIVATE ${TQ_VULKAN_SOURCES})
-    target_link_libraries(turboquant PRIVATE Vulkan::Vulkan)
-    target_link_libraries(turboquant_shared PRIVATE Vulkan::Vulkan)
-    target_compile_definitions(turboquant PRIVATE TQ_BUILD_VULKAN=1)
-    target_compile_definitions(turboquant_shared PRIVATE TQ_BUILD_VULKAN=1)
-    message(STATUS "TurboQuant: Vulkan backend enabled")
+    find_package(Vulkan QUIET)
+    if(Vulkan_FOUND)
+        file(GLOB TQ_VULKAN_SOURCES src/backend/vulkan/*.c)
+        target_sources(turboquant PRIVATE ${TQ_VULKAN_SOURCES})
+        target_sources(turboquant_shared PRIVATE ${TQ_VULKAN_SOURCES})
+        target_link_libraries(turboquant PRIVATE Vulkan::Vulkan)
+        target_link_libraries(turboquant_shared PRIVATE Vulkan::Vulkan)
+        target_compile_definitions(turboquant PRIVATE TQ_BUILD_VULKAN=1)
+        target_compile_definitions(turboquant_shared PRIVATE TQ_BUILD_VULKAN=1)
+        message(STATUS "TurboQuant: Vulkan backend enabled (${Vulkan_LIBRARY})")
+    else()
+        message(WARNING "TurboQuant: TQ_BUILD_VULKAN=ON but Vulkan SDK not found. "
+                        "Install Vulkan SDK or set VULKAN_SDK environment variable. "
+                        "Building without Vulkan backend.")
+    endif()
 endif()
 
 # ROCm/HIP backend (AMD GPU)
 if(TQ_BUILD_ROCM)
-    find_package(hip REQUIRED)
-    file(GLOB TQ_ROCM_SOURCES src/backend/rocm/*.cpp)
-    target_sources(turboquant PRIVATE ${TQ_ROCM_SOURCES})
-    target_sources(turboquant_shared PRIVATE ${TQ_ROCM_SOURCES})
-    target_link_libraries(turboquant PRIVATE hip::device)
-    target_link_libraries(turboquant_shared PRIVATE hip::device)
-    target_compile_definitions(turboquant PRIVATE TQ_BUILD_ROCM=1)
-    target_compile_definitions(turboquant_shared PRIVATE TQ_BUILD_ROCM=1)
-    message(STATUS "TurboQuant: ROCm/HIP backend enabled")
+    find_package(hip QUIET)
+    if(hip_FOUND)
+        file(GLOB TQ_ROCM_SOURCES src/backend/rocm/*.cpp)
+        target_sources(turboquant PRIVATE ${TQ_ROCM_SOURCES})
+        target_sources(turboquant_shared PRIVATE ${TQ_ROCM_SOURCES})
+        target_link_libraries(turboquant PRIVATE hip::device)
+        target_link_libraries(turboquant_shared PRIVATE hip::device)
+        target_compile_definitions(turboquant PRIVATE TQ_BUILD_ROCM=1)
+        target_compile_definitions(turboquant_shared PRIVATE TQ_BUILD_ROCM=1)
+        message(STATUS "TurboQuant: ROCm/HIP backend enabled")
+    else()
+        message(WARNING "TurboQuant: TQ_BUILD_ROCM=ON but HIP SDK not found. "
+                        "Install ROCm or set HIP_PATH. "
+                        "Building without ROCm backend.")
+    endif()
 endif()
 
 # Compiler warnings
@@ -185,6 +197,7 @@ if(TQ_BUILD_TESTS)
     include(FetchContent)
     FetchContent_Declare(googletest
         URL https://github.com/google/googletest/archive/refs/tags/v1.14.0.tar.gz
+        DOWNLOAD_EXTRACT_TIMESTAMP TRUE
     )
     set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
     FetchContent_MakeAvailable(googletest)