[SYCL] Fix memory leak for sub-devices (#20370)
Current `device_impl` implementation assumes shared ownership and
manages the handle via `urRetain`/`urRelease` in constructor/destructor.
Whenever we get temporary device handles via
`urDeviceGet`/`urDevicePartition` (which implicitly return device handle
with `refcount == 1`) and wrap those handles in `device_impl`, we have
to release temporary handles at
the end of scope to avoid memory leak.
It's done here for devices:
https://github.com/intel/llvm/blob/6b29cf120c267118dc8ad737e54e8b844bfb4e06/sycl/source/detail/platform_impl.cpp#L560-L563
Same needs to be done when we create sub-devices. But currently we were
missing release calls for temporary handles after creating `device_impl`
objects wrapping those handles. This PR fixes that issue by releasing
temporary handles at the end of the scope.
