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%

src/machine/machine_state.rs

@@ -16,7 +16,6 @@ use crate::parser::ast::*;
 use crate::read::TermWriteResult;
 use crate::types::*;
 
-use crate::parser::dashu::Integer;
 
 use indexmap::IndexMap;
 
@@ -1112,23 +1111,23 @@ impl MachineState {
 #[allow(clippy::upper_case_acronyms)]
 #[derive(Debug)]
 pub(crate) struct CWIL {
-    local_count: Integer,
-    pub(crate) global_count: Integer,
-    limits: Vec<(Integer, usize)>,
+    local_count: u128,
+    pub(crate) global_count: u128,
+    limits: Vec<(u128, usize)>,
     pub(crate) inference_limit_exceeded: bool,
 }
 
 impl CWIL {
     pub(crate) fn new() -> Self {
         CWIL {
-            local_count: Integer::from(0),
-            global_count: Integer::from(0),
+            local_count: 0,
+            global_count: 0,
             limits: vec![],
             inference_limit_exceeded: false,
         }
     }
 
-    pub(crate) fn add_limit(&mut self, mut limit: Integer, block: usize) -> &Integer {
+    pub(crate) fn add_limit(&mut self, mut limit: u128, block: usize) -> u128 {
         limit += &self.local_count;
 
         match self.limits.last() {
@@ -1136,23 +1135,23 @@ impl CWIL {
             _ => self.limits.push((limit, block)),
         }
 
-        &self.local_count
+        self.local_count
     }
 
     #[inline(always)]
-    pub(crate) fn remove_limit(&mut self, block: usize) -> &Integer {
+    pub(crate) fn remove_limit(&mut self, block: usize) -> u128 {
         if let Some((_, bl)) = self.limits.last() {
             if bl == &block {
                 self.limits.pop();
             }
         }
 
-        &self.local_count
+        self.local_count
     }
 
     #[inline(always)]
     pub(crate) fn reset(&mut self) {
-        self.local_count = Integer::from(0);
+        self.local_count = 0;
         self.limits.clear();
         self.inference_limit_exceeded = false;
     }