[NATIVECPU] Fix coverity warnings when handling reqd_work_group_size

[PietroGhg]

This PR fixes some new coverity warnings reported in the Native CPU adapter:

• mdNode is defined with const auto& to avoid copies
• hProgram uses unique_ptr to avoid leaks if we return early

This PR also adds the inclusion of <array> in program.hpp, fixing a build error on Windows. llvm PR: https://github.com/intel/llvm/pull/13805

[kbenzie]

@PietroGhg all code owners must have approved PR's before adding the ready to merge label.

[PietroGhg]

@PietroGhg all code owners must have approved PR's before adding the ready to merge label.

sorry @kbenzie, got all the approvals now