Change the type of Session.Counter.Value to BigInteger

### I am planning on implementing this myself

Yes

### Describe your request

For a certain project I'm working on, I am using session counters that will very quickly go above the 32 bit integer limit. For the purposes of this project, it's important that I have the ability to store an arbitrarily large number. Currently, the only feasible way I could see of making this work while maintaining mod interoperability is to directly patch the class itself.

### Additional context

_No response_