Paging (NGAP): add paging encode/decode library and unit tests (3GPP TS 38.413)

- Refactor ngap_paging_ind_t (openair2/COMMON/ngap_messages_types.h):
  - optional paging_drx and paging_priority as pointers
  - TAI list as tai_list[] and n_tai
  - add optional IEs: Paging Origin, Paging Attempt Information,
    UE Radio Capability for Paging.
  - Introduce nr_tai_t, ngap_paging_attempt_info_t, ngap_paging_origin_t;
  - generate paging enums via FOREACH macros.
- Add NGAP Paging encode/decode/eq/free in openair3/NGAP/ngap_gNB_paging.c
  (encode_ng_paging, decode_ng_paging, eq_ng_paging, free_ng_paging).
- Replace inline Paging decode in ngap_gNB_handle_paging() with
  decode_ng_paging() and add error handling; add eq_ngap_plmn() in
  ngap_common.
- Update rrc_gNB_NGAP.c to use tai_list/n_tai and optional paging_drx
  when forwarding paging to F1AP.
- Add ASN.1 includes for Paging in ngap_msg_includes.h; register
  ngap_gNB_paging.c in root CMakeLists.txt.
- Add NGAP unit test (openair3/NGAP/tests/ngap_lib_test.c): encode/decode
  roundtrip for Paging; tests subdirectory and executable under
  ENABLE_TESTS in openair3/NGAP/CMakeLists.txt.

CMakeLists.txt

@@ -434,6 +434,7 @@ add_library(ngap
   ${NGAP_DIR}/ngap_gNB_handlers.c
   ${NGAP_DIR}/ngap_gNB_itti_messaging.c
   ${NGAP_DIR}/ngap_gNB_management_procedures.c
+  ${NGAP_DIR}/ngap_gNB_paging.c
   ${NGAP_DIR}/ngap_gNB_nas_procedures.c
   ${NGAP_DIR}/ngap_gNB_pdu_session_management.c
   ${NGAP_DIR}/ngap_gNB_nnsf.c
@@ -443,6 +444,9 @@ add_library(ngap
   )
 target_link_libraries(ngap PUBLIC asn1_ngap)
 target_link_libraries(ngap PRIVATE asn1_lte_rrc_hdrs asn1_nr_rrc_hdrs)
+if(ENABLE_TESTS)
+  target_compile_definitions(ngap PRIVATE ENABLE_TESTS)
+endif()
 
 #M2AP
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