Further Improved Convergence test

[jp1924]

🚀 The feature, motivation and pitch

While performing PR #524, it was determined that testing the functionality of patching the Liger-Kernel onto model instances is insufficient.

(It is recommended to read the comment first) As mentioned in: https://github.com/linkedin/Liger-Kernel/pull/524#issuecomment-2764595175

Currently, the test does not separately verify the method of patching the Liger-Kernel onto already created model instances.

This is considered a blind spot of the Liger-Kernel.

Since this area is not being tested, it is anticipated that bugs like #627 will continue to occur frequently in the future.

Therefore, I propose adding a convergence test for this method.

cc: @Tcc0403