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, 2 insertions, 0 deletions

diff --git a/src/zenutil/zenutil.cpp b/src/zenutil/zenutil.cpp
index c4d01554d..032f21c9b 100644
--- a/src/zenutil/zenutil.cpp
+++ b/src/zenutil/zenutil.cpp
@@ -10,6 +10,7 @@
 #	include <zenutil/config/commandlineoptions.h>
 #	include <zenutil/rpcrecording.h>
 #	include <zenutil/splitconsole/logstreamlistener.h>
+#	include <zenutil/processmetricstracker.h>
 #	include <zenutil/wildcard.h>
 
 namespace zen {
@@ -21,6 +22,7 @@ zenutil_forcelinktests()
 	commandlineoptions_forcelink();
 	imdscredentials_forcelink();
 	logstreamlistener_forcelink();
+	processmetricstracker_forcelink();
 	s3client_forcelink();
 	sigv4_forcelink();
 	wildcard_forcelink();