fix: use explicit this-> in server_cursor lambda to silence clang-20

Clang-20 warns about unused lambda capture of 'this' in generic lambdas
even when member functions are called. Using explicit this-> makes the
dependency visible to the compiler.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Pierre-Luc Gagné

lib/include/ds_mysql/server_cursor.hpp

@@ -126,7 +126,7 @@ class server_cursor {
 
     std::expected<void, std::string> bind_results() {
         [this]<std::size_t... Is>(std::index_sequence<Is...>) {
-            (setup_bind<std::tuple_element_t<Is, RowType>>(Is), ...);
+            (this->setup_bind<std::tuple_element_t<Is, RowType>>(Is), ...);
         }(std::make_index_sequence<N>{});
 
         if (mysql_stmt_bind_result(stmt_.get(), result_binds_.data())) {