Add GpuBuffer class (#423)

* Renamed and moved mem alloc functions into the `mscclpp::detail::`
namespace (now `mscclpp::detail::gpuCalloc*<T>()`)
* Deprecated constructor-calling mem alloc functions
(`mscclpp::makeShared*<T>()` and `mscclpp::makeUnique*<T>()`)
* Added a new `mscclpp::GpuBuffer<T>()` class that should be used in
general for allocating communication buffers
* Added a new `mscclpp.utils.GpuBuffer` Python class that inherits
`cupy.ndarray` and allocates using `mscclpp::gpuMemAlloc`
* Renamed `mscclpp::memcpyCuda*<T>()` functions into
`mscclpp::gpuMemcpy*<T>()` for name consistency
* A few fixes in NVLS memory allocation
* Tackled minor compiler warnings

python/mscclpp/__init__.py

@@ -24,9 +24,9 @@ from ._mscclpp import (
     Executor,
     ExecutionPlan,
     PacketType,
+    RawGpuBuffer,
     version,
     is_nvls_supported,
-    alloc_shared_physical_cuda,
     npkit,
 )