Cross-platform process metrics support (#887)

- **Cross-platform `GetProcessMetrics`**: Implement Linux (`/proc/{pid}/stat`, `/proc/{pid}/statm`, `/proc/{pid}/status`) and macOS (`proc_pidinfo(PROC_PIDTASKINFO)`) support for CPU times and memory metrics. Fix Windows to populate the `MemoryBytes` field (was always 0). All platforms now set `MemoryBytes = WorkingSetSize`.
- **`ProcessMetricsTracker`**: Experimental utility class (`zenutil`) that periodically samples resource usage for a set of tracked child processes. Supports both a dedicated background thread and an ASIO steady_timer mode. Computes delta-based CPU usage percentage across samples, with batched sampling (8 processes per tick) to limit per-cycle overhead.
- **`ProcessHandle` documentation**: Add Doxygen comments to all public methods describing platform-specific behavior.
- **Cleanup**: Remove unused `ZEN_RUN_TESTS` macro (inlined at its single call site in `zenserver/main.cpp`), remove dead `#if 0` thread-shutdown workaround block.
- **Minor fixes**: Use `HttpClientAccessToken` constructor in hordeclient instead of setting private members directly. Log ASIO version at startup and include it in the server settings list.

1 files changed, 3 insertions, 21 deletions

diff --git a/src/zenserver/main.cpp b/src/zenserver/main.cpp
index dff162b1c..00b7a67d7 100644
--- a/src/zenserver/main.cpp
+++ b/src/zenserver/main.cpp
@@ -249,7 +249,9 @@ test_main(int argc, char** argv)
 
 	zen::MaximizeOpenFileCount();
 
-	return ZEN_RUN_TESTS(argc, argv);
+	zen::testing::TestRunner Runner;
+	Runner.ApplyCommandLine(argc, argv);
+	return Runner.Run();
 }
 #endif
 
@@ -267,26 +269,6 @@ main(int argc, char* argv[])
 	using namespace zen;
 	using namespace std::literals;
 
-	// note: doctest has locally (in thirdparty) been fixed to not cause shutdown
-	// 		 crashes due to TLS destructors
-	//
-	// mimalloc on the other hand might still be causing issues, in which case
-	// we should work out either how to eliminate the mimalloc dependency or how
-	// to configure it in a way that doesn't cause shutdown issues
-
-#if 0 	
-	auto _ = zen::MakeGuard([] {
-		// Allow some time for worker threads to unravel, in an effort
-		// to prevent shutdown races in TLS object destruction, mainly due to
-		// threads which we don't directly control (Windows thread pool) and
-		// therefore can't join.
-		//
-		// This isn't a great solution, but for now it seems to help reduce
-		// shutdown crashes observed in some situations.
-		WaitForThreads(1000);
-	});
-#endif
-
 	enum
 	{
 		kHub,