Use signed in a bunch of places

src/server.cpp

@@ -512,14 +512,14 @@ void Server::process_connection_batch(
     std::span<const int> events) {
 
   // First process writes for each connection
-  for (size_t i = 0; i < batch.size(); ++i) {
+  for (int i = 0; i < static_cast<int>(batch.size()); ++i) {
     if (batch[i]) {
       process_connection_writes(batch[i], events[i]);
     }
   }
 
   // Then process reads for each connection
-  for (size_t i = 0; i < batch.size(); ++i) {
+  for (int i = 0; i < static_cast<int>(batch.size()); ++i) {
     if (batch[i]) {
       process_connection_reads(batch[i], events[i]);
     }