memory usage of different length

Hello, I found "max_prompt_length" and "max_completion_length" do not affect the memory usage.

For example:
Case 1：max_prompt_length = 1024, max_completion_length=2048
Case 2：max_prompt_length = 256, max_completion_length=512

I found the memory usage is same.

Start by reproducing the reported memory usage with max_prompt_length values of 1024 and 256 and max_completion_length values of 2048 and 512. Trace where these parameters are consumed and determine whether the differing configurations should change memory usage; done means the behavior is explained and, if it is a bug, covered by a regression test.

Written by the indexing model from the issue text.