Fix share model_registry with worker processes

[stanfea]

MultiLLM.model_registry was empty in the process scope need to share it with the worker processes

Fixes:

multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/opt/homebrew/Cellar/[email protected]/3.11.6/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
                    ^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/[email protected]/3.11.6/Frameworks/Python.framework/Versions/3.11/lib/python3.11/multiprocessing/pool.py", line 51, in starmapstar
    return list(itertools.starmap(args[0], args[1]))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/stan/Library/Caches/pypoetry/virtualenvs/freedo-pitch-bot-server-_WifoDOq-py3.11/lib/python3.11/site-packages/multillm/MultiLLM.py", line 45, in task
    model = MultiLLM.model_registry[model_name]
            ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^
KeyError: 'BARD'
"""