Fix: Forward SplitRendBFI to lc3plus decoding routine and add LC3plus PLC test coverage

Reason why this change is needed

• To fix & test Split-Rendering concealment when LC3plus is used as transport codec

Description of the change

• Split BFI flag is forwarded to the LC3plus decoder wrapper to trigger the concealment function if set
• Test coverage of split rendering PLC configs are extended to cover LC3plus configs

Affected operating points

• Concealment for split-rendering bitstreams when LC3plus is used

How to test

• python3 -m pytest tests/split_rendering/test_split_rendering.py -k plc