Replace 0xFFFFFFFF sentinel with explicit getOutboundTotal()

Instead of overloading getOutboundCount() with a magic sentinel value,
add a dedicated getOutboundTotal() method to the PacketManager interface
that returns the total queue size without time filtering.

This eliminates the fragile convention that caused the regression and
makes the two operations — time-filtered count vs total count —
explicitly separate in the API.

examples/companion_radio/MyMesh.cpp

@@ -1712,7 +1712,7 @@ void MyMesh::handleCmdFrame(size_t len) {
       out_frame[i++] = STATS_TYPE_CORE;
       uint16_t battery_mv = board.getBattMilliVolts();
       uint32_t uptime_secs = _ms->getMillis() / 1000;
-      uint8_t queue_len = (uint8_t)_mgr->getOutboundCount(0xFFFFFFFF);
+      uint8_t queue_len = (uint8_t)_mgr->getOutboundTotal();
       memcpy(&out_frame[i], &battery_mv, 2); i += 2;
       memcpy(&out_frame[i], &uptime_secs, 4); i += 4;
       memcpy(&out_frame[i], &_err_flags, 2); i += 2;