Fix for nr_ulsch_16/64/256qam_llr reading/writing past buffer size on x86 and ARM.

This fixes out-of-bounds access: nr_ulsch_16qam_llr, nr_ulsch_64qam_llr and nr_ulsch_256qam_llr.
For 256qam this also fixes incorrect llr calculation on arm: the existing AVX code for 2 REs
case produced results not in line with the rest of the code. A testcase check_2_res_256_qam was
added to visualise the differences which can later be used to revive AVX acceleration for 2REs case.

openair1/PHY/CMakeLists.txt

 add_subdirectory(nr_phy_common)
 add_subdirectory(TOOLS)
+add_subdirectory(NR_TRANSPORT)

openair1/PHY/NR_TRANSPORT/CMakeLists.txt

+if (ENABLE_TESTS)
+  add_subdirectory(tests)
+endif()

openair1/PHY/NR_TRANSPORT/tests/CMakeLists.txt

+add_executable(test_llr test_llr.cpp)
+target_link_libraries(test_llr PRIVATE PHY_NR GTest::gtest minimal_lib)
+add_dependencies(tests test_llr)
+add_test(NAME test_llr
+  COMMAND ./test_llr)