SYCL test: add compile-time conformance checks for group/sub_group comparison operators

[Copilot]

This addresses the linked review feedback by adding compile-time coverage for SYCL 2020 comparison-operator requirements that were not validated in group.cpp. The change is scoped to the single requested comment.

• What was missing

  • sycl/test/basic_tests/group.cpp only validated host runtime behavior for get_local_id / get_local_linear_id.
  • It did not assert API-shape guarantees for group / sub_group equality operators.

• What changed

  • Added compile-time traits and static_asserts for sycl::group<1> and sycl::sub_group to verify:
    • no member operator== / operator!= (hidden-friend style),
    • comparison expressions return bool,
    • comparison expressions are noexcept.

• Example of added coverage

  static_assert(!has_member_equal<Group>::value);
  static_assert(std::is_same_v<decltype(std::declval<const Group &>() ==
                                        std::declval<const Group &>()),
                               bool>);
  static_assert(noexcept(std::declval<const Group &>() ==
                         std::declval<const Group &>()));