Multiple bug fixes

[acezxn]

The incorrect logic comes from the if statement added that supposed to ensure candidate_node is not nullish. Additionally, the ts analyzer overwrites previous scope_env data when parsing new files.

Besides bug fixes, the prompt for the intra dataflow analyzer is improved so it is more relavent to the JavaScript language and has more clarity.

[chengpeng-wang]

Hi @acezxn Thank you for your contribution. Could you resolve this type check error first?

src/llmtool/dfbscan/intra_dataflow_analyzer.py:152: error: Need type annotation for "current_path"  [var-annotated]
src/llmtool/dfbscan/intra_dataflow_analyzer.py:179: error: Item "str" of "list[Any] | str | Any" has no attribute "append"  [union-attr]
Found 2 errors in 1 file (checked 47 source files)
Error: Process completed with exit code 1.