Relax ID type

**Is your feature request related to a problem? If so, please describe.**
Relax the particle `id` type to any integer or any type.

@DavidSagan and @ChristopherMayes use any `int` type in the `BeamPhysics` extension for particle `id`s: https://github.com/openPMD/openPMD-standard/pull/183

**Describe the solution you'd like**
Relax to `intX` or even any type to be fully compatible with the base standard.

**Describe alternatives you've considered**
In reality, `uint64_t` is the only type I can truly use in parallel PIC simulations. What are you using these days @ChristopherMayes?

**Additional context**
Relaxing the type for "small" integer types is probably a bit of a corner case for "small"/non-parallel simulations (<2e9 particles) and complicates reading (check for type first) a bit.