Migrate codebase to std::string_view (except z3++.h) (#8266)

* Initial plan

* Update z3 codebase to use std::string_view (except z3++.h)

- Updated params.cpp/h to use string_view internally for parameter descriptions
- Updated trace.h/cpp to accept string_view for trace tag functions
- Updated hash.h/cpp to use string_view for string_hash function
- Updated all callers of string_hash to use string_view
- Properly handled nullptr to empty string_view conversions
- All tests passing

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Add missing string_view includes to headers

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

src/sat/sat_proof_trim.h

@@ -40,7 +40,7 @@ namespace sat {
         
         struct hash {
             unsigned operator()(literal_vector const& v) const {
-                return string_hash((char const*)v.begin(), v.size()*sizeof(literal), 3);
+                return string_hash(std::string_view((char const*)v.begin(), v.size()*sizeof(literal)), 3);
             }
         };
         struct eq {

src/sat/smt/bv_solver.cpp

@@ -711,7 +711,7 @@ namespace bv {
             hash(solver& s) :s(s) {}
             bool operator()(theory_var v) const {
                 literal_vector const& a = s.m_bits[v];
-                return string_hash(reinterpret_cast<char*>(a.data()), a.size() * sizeof(sat::literal), 3);
+                return string_hash(std::string_view(reinterpret_cast<char*>(a.data()), a.size() * sizeof(sat::literal)), 3);
             }
         };
         eq eq_proc(*this);