http: enclose libevent-dependent code in a namespace

This commit is a no-op to isolate HTTP methods and objects that
depend on libevent. Following commits will add replacement objects
and methods in a new namespace for testing and review before
switching over the server.

src/httpserver.cpp

@@ -46,6 +46,7 @@
 #include <support/events.h>
 
 using common::InvalidPortErrMsg;
+using http_libevent::HTTPRequest;
 
 /** Maximum size of http request (request line + headers) */
 static const size_t MAX_HEADERS_SIZE = 8192;
@@ -381,6 +382,7 @@ static void libevent_log_cb(int severity, const char *msg)
     }
 }
 
+namespace http_libevent {
 bool InitHTTPServer(const util::SignalInterrupt& interrupt)
 {
     if (!InitHTTPAllowList())
@@ -497,6 +499,7 @@ struct event_base* EventBase()
 {
     return eventBase;
 }
+} // namespace http_libevent
 
 static void httpevent_callback_fn(evutil_socket_t, short, void* data)
 {
@@ -524,6 +527,8 @@ void HTTPEvent::trigger(struct timeval* tv)
     else
         evtimer_add(ev, tv); // trigger after timeval passed
 }
+
+namespace http_libevent {
 HTTPRequest::HTTPRequest(struct evhttp_request* _req, const util::SignalInterrupt& interrupt, bool _replySent)
     : req(_req), m_interrupt(interrupt), replySent(_replySent)
 {
@@ -686,6 +691,7 @@ std::optional<std::string> GetQueryParameterFromUri(const char* uri, const std::
 
     return result;
 }
+} // namespace http_libevent
 
 void RegisterHTTPHandler(const std::string &prefix, bool exactMatch, const HTTPRequestHandler &handler)
 {