It’s a mouse. If you think feeding one to a snake is ethical, then it’s a little strange this would be unethical. At least the human has the mouse’s wellbeing at heart.

The term "lab rats" exists for a reason. This is in the bottom 10% of weird shit people do to animals for research.

If we can even have robots that can perform critical surgeries with total precision and save more lives would that be bad?

That ship sailed a long time ago. Science decided that killing mice for experiments (regardless of the experiment) is fine. In fact, a large amount of the mice killed are just redundant (not needed for a particular experiment)