fix: isCuMemMapAllocated crashes on non-NVLS systems even with MSCCLPP_FORCE_DISABLE_NVLS=true (#790)

- [x] Fix `isCuMemMapAllocated()` to just return `true/false` without
throwing when NVLS is not supported
- [x] Fix `isNvlsSupported()` caching bug where `result`/`isChecked`
were never updated
- [x] Restore `[[maybe_unused]]` on `result` and `isChecked` statics —
needed in HIP/ROCm env where `CUDA_NVLS_API_AVAILABLE` is not defined
and the variables would otherwise be unused
- [x] Run linter (`./tools/lint.sh`)

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Binyang2014 <9415966+Binyang2014@users.noreply.github.com>

Author: Copilot

src/core/gpu_utils.cc

@@ -283,7 +283,9 @@ bool isNvlsSupported() {
     MSCCLPP_CUDATHROW(cudaGetDevice(&deviceId));
     MSCCLPP_CUTHROW(cuDeviceGet(&dev, deviceId));
     MSCCLPP_CUTHROW(cuDeviceGetAttribute(&isMulticastSupported, CU_DEVICE_ATTRIBUTE_MULTICAST_SUPPORTED, dev));
-    return isMulticastSupported == 1;
+    result = (isMulticastSupported == 1);
+    isChecked = true;
+    return result;
   }
   return result;
 #endif
@@ -300,9 +302,6 @@ bool isCuMemMapAllocated([[maybe_unused]] void* ptr) {
     return false;
   }
   MSCCLPP_CUTHROW(cuMemRelease(handle));
-  if (!isNvlsSupported()) {
-    throw Error("cuMemMap is used in env without NVLS support", ErrorCode::InvalidUsage);
-  }
   return true;
 #endif
 }