Fix: maintain node order in JSON export

[rahulsolanki001]

Description

This pull request addresses the issue where the JSON export from the drawflow library did not maintain the user-defined order of nodes after adding, removing, or repositioning them. The changes made ensure that nodes are exported in the correct sequence as per their connection sequence in the UI.

Changes Made

• Ensured nodes are ordered correctly in the JSON export.
• Used a traversal algorithm to determine the correct order of nodes.
• Updated the export functionality to reflect the correct node sequence.

Fixes #864 order of the nodes not correct when changing in the UI & then exporting it

[jerosoler]

Thanks for the PR, I'll check it out. Even though I've never had a problem. But it is true that a JSON does not return correctly.

Be careful that sometimes the order is correct, but browsers display them in an orderly manner.