switch from Integer to u128

switch from Integer to u128

- u128 is only 16 bytes instead of 24
- incrementing u128 does not involve heap allocations
- u128 should be sufficent
 it would take more than 2 sextilion years to overflow if we would be incrementing it every tick at 5GHz
   i.e. 2^128-1 / 5 GHz / 60 / 60 / 24 / 356 > 2 sextilion

before this ~3.2% of the execution time of the program in https://github.com/mthom/scryer-prolog/issues/3265#issuecomment-4103176469 was spend in the increment_call_count function, after this change it's down to 0.3%