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, 1 insertions, 1 deletions

diff --git a/src/zenserver/compute/computeserver.cpp b/src/zenserver/compute/computeserver.cpp
index c64f081b3..2ac3de599 100644
--- a/src/zenserver/compute/computeserver.cpp
+++ b/src/zenserver/compute/computeserver.cpp
@@ -674,7 +674,7 @@ ZenComputeServer::PostAnnounce()
 		{
 			ZEN_ERROR("failed to notify coordinator at '{}': HTTP error {} - {}",
 					  m_CoordinatorEndpoint,
-					  Result.Error->ErrorCode,
+					  static_cast<int>(Result.Error->ErrorCode),
 					  Result.Error->ErrorMessage);
 		}
 		else if (!IsHttpOk(Result.StatusCode))