Refactor of includes in gNB/UE for improved header management

This merge request implements changes suggested by the Include What You Use (IWYU) open source tool to streamline the project’s header file usage.

The adjustments ensure that each file includes only the necessary headers for the symbols it uses, making the code more efficient and maintainable. Unnecessary includes have been removed, and missing headers have been added where required. This improves modularity and reduces inter-dependencies between files, helping to avoid future build issues caused by unused or missing includes.

Each output has been manually reviewed.

Followed a similar approach as in !2953 (merged).

Affected folders/files:

• NR_MAC_gNB/main.c
• nr-softmodem.c
• unitary simulators: nr_dlsim, nr_ulsim, prachsim
• openair2/RRC/NR
• openair3/NGAP
• openair2/LAYER2/nr_pdcp
• openair2/SDAP/nr_sdap