Fix implicit conversion warnings: use UINT_MAX instead of -1 for unsi… (#8342)

* Fix implicit conversion warnings: use UINT_MAX instead of -1 for unsigned variables

Replace implicit conversion from negative literal to unsigned type
with explicit UINT_MAX constant to eliminate compiler warnings.

Fixed 10 instances across 6 files:
- src/ast/rewriter/bv_rewriter.cpp: 1 instance
- src/ast/sls/sls_bv_tracker.h: 2 instances
- src/math/lp/dioph_eq.cpp: 3 instances
- src/math/lp/lp_primal_core_solver.h: 2 instances
- src/muz/transforms/dl_mk_array_instantiation.cpp: 1 instance
- src/muz/transforms/dl_mk_synchronize.cpp: 1 instance

These changes preserve the exact same runtime behavior (UINT_MAX
equals the wrapped value of -1 for unsigned types) while making
the code more explicit and warning-free.

* Update bv_rewriter.cpp

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

src/muz/transforms/dl_mk_array_instantiation.cpp

@@ -277,7 +277,7 @@ namespace datalog {
                 new_args.push_back(arg_correspondance[i][chosen[i]].get());
             }
             res.push_back(create_pred(old_pred, new_args));
-            unsigned pos=-1;
+            unsigned pos = UINT_MAX;
             do {
                 pos++;
                 if(pos==chosen.size()){

src/muz/transforms/dl_mk_synchronize.cpp

@@ -290,7 +290,7 @@ namespace datalog {
         bool_vector new_tail_neg;
         new_tail.resize(product_tail_length);
         new_tail_neg.resize(product_tail_length);
-        unsigned tail_idx = -1;
+        unsigned tail_idx = UINT_MAX;
         if (has_recursion) {
             add_rec_tail(recursive_calls, new_tail, new_tail_neg, tail_idx);
         }