[SYCL][NFC] Refactor IPC for memory

[slawekptak]

List of changes:

• Introduce a common header to be used by all IPC features going forward.
• A new ipc::memory namespace with all of the functions related to IPC for memory. The ipc_memory namespace becomes deprecated and ipc::memory should be used instead.

[Copilot]

Pull request overview

This PR refactors the SYCL experimental IPC memory API by introducing a shared IPC “common” header and a new sycl::ext::oneapi::experimental::ipc::memory namespace, while keeping the legacy ipc_memory namespace as a compatibility layer.

Changes:

• Add a new common IPC header defining ipc::handle and shared handle data types.
• Implement ipc::memory::{get, put, close} and forward legacy ipc_memory::{get, put, close} to the new implementation.
• Extend the public header with ipc::memory convenience overloads (implicit default context/device, open helpers).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
sycl/source/ipc_memory.cpp	Implements the new ipc::memory API and forwards legacy ipc_memory entry points to shared helpers.
sycl/include/sycl/ext/oneapi/experimental/ipc_memory.hpp	Exposes the new ipc::memory API surface and retains the legacy ipc_memory API in the same header.
sycl/include/sycl/ext/oneapi/experimental/detail/ipc_common.hpp	Introduces a shared IPC handle/type definition intended for reuse across IPC features.

Comments suppressed due to low confidence (1)

sycl/include/sycl/ext/oneapi/experimental/ipc_memory.hpp:108

• The PR description says ext::oneapi::experimental::ipc_memory is deprecated in favor of ext::oneapi::experimental::ipc::memory, but the header does not annotate the legacy API with __SYCL_DEPRECATED(...) (or similar). If deprecation is intended, please add the attribute/messages on the legacy declarations (and adjust tests accordingly).

namespace ext::oneapi::experimental::ipc_memory {

using handle_data_t = std::vector<std::byte>;

#if __cpp_lib_span
using handle_data_view_t = std::span<const std::byte, std::dynamic_extent>;
#endif

struct handle {