HttpClient using libcurl, Unix Sockets for HTTP. HTTPS support (#770)

The main goal of this change is to eliminate the cpr back-end altogether and replace it with the curl implementation. I would expect to drop cpr as soon as we feel happy with the libcurl back-end. That would leave us with a direct dependency on libcurl only, and cpr can be eliminated as a dependency.

### HttpClient Backend Overhaul
- Implemented a new **libcurl-based HttpClient** backend (`httpclientcurl.cpp`, ~2000 lines)
  as an alternative to the cpr-based one
- Made HttpClient backend **configurable at runtime** via constructor arguments
  and `-httpclient=...` CLI option (for zen, zenserver, and tests)
- Extended HttpClient test suite to cover multipart/content-range scenarios

### Unix Domain Socket Support
- Added Unix domain socket support to **httpasio** (server side)
- Added Unix domain socket support to **HttpClient**
- Added Unix domain socket support to **HttpWsClient** (WebSocket client)
- Templatized `HttpServerConnectionT<SocketType>` and `WsAsioConnectionT<SocketType>`
  to handle TCP, Unix, and SSL sockets uniformly via `if constexpr` dispatch

### HTTPS Support
- Added **preliminary HTTPS support to httpasio** (for Mac/Linux via OpenSSL)
- Added **basic HTTPS support for http.sys** (Windows)
- Implemented HTTPS test for httpasio
- Split `InitializeServer` into smaller sub-functions for http.sys

### Other Notable Changes
- Improved **zenhttp-test stability** with dynamic port allocation
- Enhanced port retry logic in http.sys (handles ERROR_ACCESS_DENIED)
- Fatal signal/exception handlers for backtrace generation in tests
- Added `zen bench http` subcommand to exercise network + HTTP client/server communication stack

1 files changed, 17 insertions, 6 deletions

diff --git a/src/zenhttp/httpserver.cpp b/src/zenhttp/httpserver.cpp
index 9bae95690..1a0018908 100644
--- a/src/zenhttp/httpserver.cpp
+++ b/src/zenhttp/httpserver.cpp
@@ -1044,13 +1044,16 @@ HttpServer::OnGetExternalHost() const
 std::string
 HttpServer::GetServiceUri(const HttpService* Service) const
 {
+	const char* Scheme = (m_EffectiveHttpsPort > 0) ? "https" : "http";
+	int			Port   = (m_EffectiveHttpsPort > 0) ? m_EffectiveHttpsPort : m_EffectivePort;
+
 	if (Service)
 	{
-		return fmt::format("http://{}:{}{}", m_ExternalHost, m_EffectivePort, Service->BaseUri());
+		return fmt::format("{}://{}:{}{}", Scheme, m_ExternalHost, Port, Service->BaseUri());
 	}
 	else
 	{
-		return fmt::format("http://{}:{}", m_ExternalHost, m_EffectivePort);
+		return fmt::format("{}://{}:{}", Scheme, m_ExternalHost, Port);
 	}
 }
 
@@ -1152,9 +1155,13 @@ CreateHttpServerClass(const std::string_view ServerClass, const HttpServerConfig
 	if (ServerClass == "asio"sv)
 	{
 		ZEN_INFO("using asio HTTP server implementation")
-		return CreateHttpAsioServer(AsioConfig{.ThreadCount		  = Config.ThreadCount,
-											   .ForceLoopback	  = Config.ForceLoopback,
-											   .IsDedicatedServer = Config.IsDedicatedServer});
+		return CreateHttpAsioServer(AsioConfig {
+			.ThreadCount = Config.ThreadCount, .ForceLoopback = Config.ForceLoopback, .IsDedicatedServer = Config.IsDedicatedServer,
+			.UnixSocketPath = Config.UnixSocketPath,
+#if ZEN_USE_OPENSSL
+			.HttpsPort = Config.HttpsPort, .CertFile = Config.CertFile, .KeyFile = Config.KeyFile,
+#endif
+		});
 	}
 #if ZEN_WITH_HTTPSYS
 	else if (ServerClass == "httpsys"sv)
@@ -1165,7 +1172,11 @@ CreateHttpServerClass(const std::string_view ServerClass, const HttpServerConfig
 													.IsAsyncResponseEnabled	 = Config.HttpSys.IsAsyncResponseEnabled,
 													.IsRequestLoggingEnabled = Config.HttpSys.IsRequestLoggingEnabled,
 													.IsDedicatedServer		 = Config.IsDedicatedServer,
-													.ForceLoopback			 = Config.ForceLoopback}));
+													.ForceLoopback			 = Config.ForceLoopback,
+													.HttpsPort				 = Config.HttpSys.HttpsPort,
+													.CertThumbprint			 = Config.HttpSys.CertThumbprint,
+													.CertStoreName			 = Config.HttpSys.CertStoreName,
+													.HttpsOnly				 = Config.HttpSys.HttpsOnly}));
 	}
 #endif
 	else if (ServerClass == "null"sv)