Merge remote-tracking branch 'origin/refactor-dlsch' into integration_2025_w44 (!3682)

Refactor DLSCH scheduler

Refactor the DLSCH post processor similarly to what has been done in
!3521  with the goal of saving an additional iteration through all UEs,
hopefully making the DLSCH scheduler faster.

It further includes changes to make working with and debugging multi-UE
operation easier:

- add some measurements in L1 (for total TX/RX time)
- a new option MACRLCs.[0].stats_max_ue to limit the number of UEs in
  the periodic output (default: 8, 0=disable)
- avoid stack overflow in the MAC
- fix the writing of stats to nrMAC_stats.log and nrL1_stats.log when
  the written output reduces by truncating the files
- avoid to schedule retransmission with 0 RBs.

doc/MAC/mac-usage.md

@@ -236,6 +236,9 @@ In the `MACRLCs` section of the gNB/DU configuration file:
    case RSSI reaches the threshold and prevents ADC railing. Unit depends on
    RSSI reporting config.
 * `pucch_RSSI_Threshold`: Same as above but for PUCCH
+* `stats_max_ue` (default 8): maximum number of UEs to show in periodical
+  stats; beyond this number, periodical statistics will be disabled (it can
+  still be seen in `nrMAC_stats.log`. Use `0` to disable periodical stats.
 
 In the `gNBs` section of the gNB/DU configuration file: some of the parameters
 affect RRC configuration (CellGroupConfig) of a UE, and are therefore listed