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, 57 insertions, 0 deletions

diff --git a/src/zenhttp/clients/httpclientcommon.cpp b/src/zenhttp/clients/httpclientcommon.cpp
index 6f4c67dd0..e4d11547a 100644
--- a/src/zenhttp/clients/httpclientcommon.cpp
+++ b/src/zenhttp/clients/httpclientcommon.cpp
@@ -646,6 +646,63 @@ TEST_CASE("CompositeBufferReadStream")
 	CHECK_EQ(IoHash::HashBuffer(Data), testutil::HashComposite(Data));
 }
 
+TEST_CASE("ParseContentRange")
+{
+	SUBCASE("normal range with total size")
+	{
+		auto [Offset, Length] = detail::ParseContentRange("bytes 0-99/500");
+		CHECK_EQ(Offset, 0);
+		CHECK_EQ(Length, 100);
+	}
+
+	SUBCASE("non-zero offset")
+	{
+		auto [Offset, Length] = detail::ParseContentRange("bytes 2638-5111437/44369878");
+		CHECK_EQ(Offset, 2638);
+		CHECK_EQ(Length, 5111437 - 2638 + 1);
+	}
+
+	SUBCASE("wildcard total size")
+	{
+		auto [Offset, Length] = detail::ParseContentRange("bytes 100-199/*");
+		CHECK_EQ(Offset, 100);
+		CHECK_EQ(Length, 100);
+	}
+
+	SUBCASE("no slash (total size omitted)")
+	{
+		auto [Offset, Length] = detail::ParseContentRange("bytes 50-149");
+		CHECK_EQ(Offset, 50);
+		CHECK_EQ(Length, 100);
+	}
+
+	SUBCASE("malformed input returns zeros")
+	{
+		auto [Offset1, Length1] = detail::ParseContentRange("not-bytes 0-99/500");
+		CHECK_EQ(Offset1, 0);
+		CHECK_EQ(Length1, 0);
+
+		auto [Offset2, Length2] = detail::ParseContentRange("bytes abc-def/500");
+		CHECK_EQ(Offset2, 0);
+		CHECK_EQ(Length2, 0);
+
+		auto [Offset3, Length3] = detail::ParseContentRange("");
+		CHECK_EQ(Offset3, 0);
+		CHECK_EQ(Length3, 0);
+
+		auto [Offset4, Length4] = detail::ParseContentRange("bytes 100/500");
+		CHECK_EQ(Offset4, 0);
+		CHECK_EQ(Length4, 0);
+	}
+
+	SUBCASE("single byte range")
+	{
+		auto [Offset, Length] = detail::ParseContentRange("bytes 42-42/1000");
+		CHECK_EQ(Offset, 42);
+		CHECK_EQ(Length, 1);
+	}
+}
+
 TEST_CASE("MultipartBoundaryParser")
 {
 	uint64_t Range1Offset = 2638;