This commit introduces a dedicated simulation environment to validate
the uplink MU-MIMO joint processing framework. It models a scenario
where a single gNB serves multiple spatially multiplexed UEs sharing
the exact same time and frequency resources.

The simulator executes the complete physical layer baseband pipeline:
- PUSCH data generation and LDPC encoding per UE
- OFDM modulation (TX)
- Signal propagation through a multi-path channel model
- OFDM demodulation (RX) at the gNB
- Joint PUSCH decoding, equalization, and spatial demultiplexing

Performance metrics such as scrambling errors and BLER per UE is
evaluated at the end of the simulation.
Signed-off-by: Rakesh Mundlamuri <rakesh.mundlamuri@openairinterface.org>