Add MoQ performance test client

Summary:
This adds a performance test client for MoQ/moxygen that helps determine the maximum number of subscribers that can subscribe to a given track at the relay before it affects latency.

**Features:**
- Takes relay URL, quic_transport boolean, target_subscribers, and duration flags
- Uses moq-test scheme with configurable parameters:
  - one-stream-per-group (ForwardingPreference::ONE_SUBGROUP_PER_GROUP)
  - object_interval: 33ms
  - I-frame size: 7,576 bytes
  - P-frame size: 1,894 bytes
  - 30 objects per group (1 group per second)
  - end group of 60
  - DELIVERY_TIMEOUT parameter: 10ms
- Gradually adds subscribers over 10 seconds to reach target_subscribers
- Each subscriber uses its own QUIC or WebTransport connection
- All subscribers run on a single event base
- Reports statistics every 1 second (subscriber count, objects/s, bytes/s)
- Automatically terminates if any subscriber detects a stream reset
- Prints comprehensive test summary at the end

**Implementation:**
- `MoQPerfTestClient`: Main test orchestrator managing multiple subscribers
- `SubscriberState`: Tracks state and statistics for each individual subscriber
- Uses `evb_->timer()` for scheduling periodic tasks
- Uses `loop()` instead of `loopForever()` - event loop stops when all work completes
- Calls `drain()` after subscribe so client exits when publisher ends

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Differential Revision: D86928590

Author: afrind

moxygen/MoQFramer.cpp

@@ -59,6 +59,7 @@ bool isValidGroupOrderParam(uint64_t value) {
     case folly::to_underlying(moxygen::GroupOrder::NewestFirst):
       return true;
     default:
+      XLOG(ERR) << "Invalid group order value=" << value;
       return false;
   }
   return true;

moxygen/moqtest/CMakeLists.txt

@@ -97,4 +97,37 @@ install(
     LIBRARY DESTINATION ${LIB_INSTALL_DIR}
 )
 
+
+# moqperf_test_client
+add_executable(
+  moqperf_test_client
+  MoQPerfTestClient.cpp
+  MoQPerfTestClientMain.cpp
+)
+set_target_properties(
+  moqperf_test_client
+  PROPERTIES
+    BUILD_RPATH ${DEPS_LIBRARIES_DIR}
+    INSTALL_RPATH ${DEPS_LIBRARIES_DIR}
+)
+target_include_directories(
+  moqperf_test_client PUBLIC $<BUILD_INTERFACE:${MOXYGEN_FBCODE_ROOT}>
+)
+target_compile_options(
+  moqperf_test_client PRIVATE
+  ${_MOXYGEN_COMMON_COMPILE_OPTIONS}
+)
+target_link_libraries(
+  moqperf_test_client PUBLIC
+  moqtest_utils
+  moxygenwtclient
+)
+
+install(
+    TARGETS moqperf_test_client
+    EXPORT moxygen-exports
+    ARCHIVE DESTINATION ${LIB_INSTALL_DIR}
+    LIBRARY DESTINATION ${LIB_INSTALL_DIR}
+)
+
 #add_subdirectory(test)