Refactor: Improve type safety and readability in dynamic do_POST wrapper

[pyob-bot]

Summary of Changes

• Refactored the _dynamic_do_POST_wrapper function within EntranceMixin to improve code clarity.
• Renamed the parameter self to instance to better reflect its usage within the wrapper function, avoiding potential confusion with the outer class scope.

Technical Impact

• Code Maintainability: Improves readability by explicitly naming the handler instance, making the logic easier to follow for future maintenance.
• Functionality: No changes to the underlying logic or behavior; the dynamic method injection remains functionally identical to the previous implementation.