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/ast/rewriter/bv_rewriter.cpp

@@ -24,7 +24,6 @@ Notes:
 #include "ast/ast_pp.h"
 
 
-
 void bv_rewriter::updt_local_params(params_ref const & _p) {
     bv_rewriter_params p(_p);
     m_hi_div0 = p.hi_div0();
@@ -683,7 +682,7 @@ unsigned bv_rewriter::propagate_extract(unsigned high, expr * arg, expr_ref & re
     bool all_numerals = true;
     unsigned removable = to_remove;
     numeral val;
-    unsigned curr_first_sz = -1;
+    unsigned curr_first_sz = UINT_MAX;
     // calculate how much can be removed
     for (unsigned i = 0; i < num; ++i) {
         expr * const curr = a->get_arg(i);

src/ast/sls/sls_bv_tracker.h

@@ -1037,7 +1037,7 @@ public:
         }
         m_temp_constants.reset();
 
-        unsigned pos = -1;
+        unsigned pos = UINT_MAX;
         if (m_ucb)
         {
             double max = -1.0;
@@ -1090,7 +1090,7 @@ public:
             return nullptr;
         m_temp_constants.reset();
         
-        unsigned cnt_unsat = 0, pos = -1;
+        unsigned cnt_unsat = 0, pos = UINT_MAX;
         for (unsigned i = 0; i < sz; ++i)
             if ((i != m_last_pos) && m_mpz_manager.neq(get_value(as[i]), m_one) && (get_random_uint(16) % ++cnt_unsat == 0)) pos = i;