Specifying "Server::stop()" as noexcept (#2451)

* The current implementation of "Server::stop()" doesn't throw an exception, so why not specify this explicitly?

* Adding the missing "noexcept" to the declaration

httplib.h

@@ -1597,7 +1597,7 @@ private:
   std::regex regex_;
 };
 
-int close_socket(socket_t sock);
+int close_socket(socket_t sock) noexcept;
 
 ssize_t write_headers(Stream &strm, const Headers &headers);
 
@@ -1734,7 +1734,7 @@ public:
 
   bool is_running() const;
   void wait_until_ready() const;
-  void stop();
+  void stop() noexcept;
   void decommission();
 
   std::function<TaskQueue *(void)> new_task_queue;
@@ -3028,8 +3028,6 @@ bool parse_range_header(const std::string &s, Ranges &ranges);
 bool parse_accept_header(const std::string &s,
                          std::vector<std::string> &content_types);
 
-int close_socket(socket_t sock);
-
 ssize_t send_socket(socket_t sock, const void *ptr, size_t size, int flags);
 
 ssize_t read_socket(socket_t sock, void *ptr, size_t size, int flags);
@@ -5422,7 +5420,7 @@ inline void mmap::close() {
 #endif
   size_ = 0;
 }
-inline int close_socket(socket_t sock) {
+inline int close_socket(socket_t sock) noexcept {
 #ifdef _WIN32
   return closesocket(sock);
 #else
@@ -5649,7 +5647,7 @@ inline bool process_client_socket(
   return callback(strm);
 }
 
-inline int shutdown_socket(socket_t sock) {
+inline int shutdown_socket(socket_t sock) noexcept {
 #ifdef _WIN32
   return shutdown(sock, SD_BOTH);
 #else
@@ -11004,7 +11002,7 @@ inline void Server::wait_until_ready() const {
   }
 }
 
-inline void Server::stop() {
+inline void Server::stop() noexcept {
   if (is_running_) {
     assert(svr_sock_ != INVALID_SOCKET);
     std::atomic<socket_t> sock(svr_sock_.exchange(INVALID_SOCKET));