Merge remote-tracking branch 'origin/rrc-sibs' into integration_2026_w16 (!3983)

Add SIB 3,4 support, configurable SIB2 and refactor CU/DU SIB management

This MR makes neighbour and inter-frequency configuration drive how
SIB2/SIB3/SIB4 are built and sent from CU to DUs. It standardizes SIB
payloads as byte_array_t with typed SIB IDs across RRC, F1AP and MAC,
reducing ad‑hoc buffer handling. Neighbour parsing, validation and
lookup are tightened.

Changes

- Minor refactor to gNB neighbour parsing and storage (shared PLMN
  extraction, safer allocation, etc).
- Represent SIB containers uniformly as byte_array_t plus nr_sib_type_t,
  and adapt F1AP, MAC and RRC users to the new container API.
- Make SIB2 cell-reselection information fully config-driven with
  explicit bounds checking and SIB2 ASN.1 building from that config.
- Generate SIB3 intra-frequency neighbours from the per-cell neighbour
  list and propagate them from CU to DU over F1, with MAC
  decoding/attaching them to SystemInformation.
- Generate SIB4 inter-frequency neighbours from a new frequency_list
  plus neighbour SIB3/SIB4 offsets, and propagate them from CU to DU
  over F1, with MAC decoding/attaching them.
- Add basic ASN.1 round-trip tests for SIB2/SIB3/SIB4 and SIB4 range
  checks, and update RRC docs to describe the neighbour/inter-frequency
  configuration model.

Testing:

1. in gNB conf file:

    cu_sibs = (2, 3, 4);

2. Update neighbour config file with SIB3/SIB4 conf:

    (see documentation)

3. run gNB and UE as usual

---

Logs & configs: see MR on Gitlab

ci-scripts/conf_files/gnb-cu.sa.band78.106prb.conf

@@ -17,6 +17,7 @@ gNBs =
     // Tracking area code, 0x0000 and 0xfffe are reserved values
     tracking_area_code  =  1;
     plmn_list = ({ mcc = 208; mnc = 99; mnc_length = 2; snssaiList = ({ sst = 1, sd = 0xffffff }) });
+    cu_sibs = ( 2, 3, 4 );
     @include "neighbour-config.conf"
 
     nr_cellid = 12345678L;

ci-scripts/conf_files/neighbour-config.conf

@@ -5,6 +5,57 @@
 #  for the 2-cell rfsim setup (gNB_ID 0xe00 & 0xb00)       #
 ############################################################
 
+############################################################
+#                           SIB2                           #
+############################################################
+
+sib2_config : {
+  q_Hyst                   = 0;
+  cellReselectionPriority  = 0;
+  threshServingLowP        = 0;
+  threshServingLowQ        = 0;
+  s_NonIntraSearchP        = -1;
+  s_NonIntraSearchQ        = -1;
+  q_RxLevMin               = -56;
+  q_QualMin                = -1;
+  s_IntraSearchP           = 22;
+  s_IntraSearchQ           = -1;
+  t_ReselectionNR          = 1;
+  deriveSSB_IndexFromCell  = 1;
+
+  speed_t_Evaluation       = 0;
+  speed_t_HystNormal       = 0;
+  speed_n_CellChangeMedium = 1;
+  speed_n_CellChangeHigh   = 2;
+  speed_sf_Medium          = 1;
+  speed_sf_High            = 0;
+};
+
+############################################################
+#      Per-frequency SIB4 inter-frequency configuration    #
+############################################################
+
+frequency_list = (
+  {
+    absoluteFrequencySSB = 621312;
+    subcarrierSpacing    = 1; # 30 kHz
+    band                 = 78;
+
+    frequency_config = (
+      {
+        cellReselectionPriority = 5;
+        threshX_HighP           = 10;
+        threshX_LowP            = 6;
+        threshX_HighQ           = -1;
+        threshX_LowQ            = -1;
+        q_OffsetFreq            = 0;
+        q_RxLevMin              = -56;
+        t_ReselectionNR         = 1;
+      }
+    );
+  }
+);
+
 neighbour_list = (
   ##########################################################
   #      Entry USED BY gNB_ID = 0xe00  (nr_cellid = 1)     #
@@ -21,6 +72,9 @@ neighbour_list = (
         band                = 78;
         plmn                = { mcc = 208; mnc = 99; mnc_length = 2 };
         tracking_area_code  = 1;
+        q_OffsetCell        = 2;
+        q_RxLevMinOffsetCell= 2;
+        q_QualMinOffsetCell = 1;
       }
     );
   },
@@ -40,6 +94,9 @@ neighbour_list = (
         band                = 78;
         plmn                = { mcc = 208; mnc = 99; mnc_length = 2 };
         tracking_area_code  = 1;
+        q_OffsetCell        = 2;
+        q_RxLevMinOffsetCell= 2;
+        q_QualMinOffsetCell = 1;
       }
     );
   }