CVE-2022-21797: joblib vulnerable to arbitrary code execution

The vulnerability stems from unsafe use of eval() in processing the pre_dispatch parameter in Parallel class initialization. The commit diff shows the vulnerable line 'pre_dispatch = eval(pre_dispatch)' was replaced with a restricted eval and later an AST-based parser. The CVE description explicitly cites improper eval usage in pre_dispatch handling as the root cause. The function responsible for processing this parameter resides in Parallel's initialization logic in parallel.py.