Fix code newline character issue introduced by astor.to_source

[redpin-pankaj]

• closes astor.to_source() seems to add a newline in the code when unparsing the AST tree #342
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.

[redpin-pankaj]

I preferred to avoid using ast.unparse() because of the warnings given in the documentation.

Also turns out that overriding the pretty_source() function when calling astor.to_source() using a simple lambda fuction which bypasses the split_lines() seems to do the trick.

Also repurposing _clean_code() method to return last line is not necessary because ast seems to remove within-expression newlines automatically, so there is no risk even if LLM is returning within-expression newlines in the code.

[gventuri]

@psaini-qontigo great job, well done! Merging!