Fix functions for casting string to var-list

[manh9203]

This pull request resolves issue #2755, which concerns the functionality for casting strings to variable lists. Here are the key updates:

• Leading spaces are now trimmed before the casting process to address the issue.
• Regarding the handling of single quotes, I conducted tests with DuckDB and found that they also interpret quotes as part of the string, so I retained them in the implementation.
• I attempted to implement escape character in this section, but encountered challenges with formatting the input string. I would need further discussion if we intend to pursue this feature at this time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.53%. Comparing base (e76c6ea) to head (797ee72).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2970   +/-   ##
=======================================
  Coverage   93.52%   93.53%           
=======================================
  Files        1119     1119           
  Lines       42991    42991           
=======================================
+ Hits        40209    40211    +2     
+ Misses       2782     2780    -2     

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