[Dev] Enhance TileLang Backend and fix a bug for INT4xINT2

[LeiWang1999]

This pull request introduces a new utility function retrieve_func_from_module and refactors existing code to use this function for retrieving the main function from an IR module. The changes ensure a more consistent and reusable approach across multiple files.

Key changes include:

Utility Function Addition:

• bitblas/utils/__init__.py: Added retrieve_func_from_module function to extract the main function from an IRModule.

Refactoring to Use New Utility Function:

• bitblas/base/common_schedules.py: Replaced direct access to the main function with retrieve_func_from_module.
• bitblas/base/utils.py: Updated multiple methods to use retrieve_func_from_module for retrieving functions from modules.
• bitblas/ops/operator.py: Replaced direct access to the main function with retrieve_func_from_module in the hardware_aware_finetune method.

Code Clean-Up:

• bitblas/ops/operator.py: Removed the update_func method as it is no longer needed due to the new utility function.