In the Perfect Imperfection by Jacek Dukaj [0] has something called "Remy's curve" [1].

On the curve you can find:

- Ultimate Computer is the computer using the best hardware as allowed by the physical constants of our universe. See also physics of computation.

- Inclusions are in essence 'pocket universes'. They are created for specific entities to run hardware in a dedicated universe with physical constants different from ours, allowing for better performance than those in our universe

- Ultimate Inclusion is the inclusion with the best possible set of physical constants in the entire multiverse

Seth Lloyd wrote a paper "Ultimate physical limits to computation" [2].

[0] https://en.wikipedia.org/wiki/Perfect_Imperfection

[1] https://en.wikipedia.org/wiki/Perfect_Imperfection#/media/Fi...

[2] https://arxiv.org/abs/quant-ph/9908043

Not neutron stars specifically, but Accelerando by Charles Stross covers this.

That was a good book, it challenged many of my assumptions.

Asimov's "The Last Question" is close, though the focus is on entropy rather than any kind of space wars.

Isn't Three Body Problem kinda like this?

Is that book worth reading ? I am half-way through and I still don't see the point ;)

I read all three books. The first was a couple of years ago. But from memory, half-way through the first should be enough to tell. If you haven't seen anything worthwhile yet, you won't by continuing.