[#1397] make message flow docs helpers robust to optional Graphviz

The scenario message-flow SVGs are documentation artifacts, so normal
scenario tests should not fail just because the Graphviz `dot` executable is
not installed.  Make `saveScenarioGraphvizFigure()` return quietly when
Graphviz is unavailable, while preserving SVG generation in docs jobs where
Graphviz is installed.

Also install the recorder source hook at `SimulationBaseClass` import time.
This lets the message-flow graph recover recorder connections even when a
recorder is created before the `SimBaseClass` instance.

Author: schaubh

src/utilities/SimulationBaseClass.py

@@ -553,6 +553,9 @@ def recorderWithSource(self, *args, _recorderMethod=recorderMethod, **kwargs):
             pass
 
 
+_ensureRecorderSourceHooks()
+
+
 class SimBaseClass:
     """Simulation Base Class"""
 

src/utilities/tests/test_SimulationBaseClass.py

@@ -305,6 +305,26 @@ def test_GetMessageConnectionGraph_with_recorder():
     assert ("dataOutMsg", "recordedMsg") in edgePairs
 
 
+def test_GetMessageConnectionGraph_with_recorder_before_sim_creation():
+    """Check recorder source tracking before creating the simulation object."""
+    cModule = cModuleTemplate.cModuleTemplate()
+    cModule.ModelTag = "cModule"
+    dataRec = cModule.dataOutMsg.recorder()
+
+    scSim = SimulationBaseClass.SimBaseClass()
+    testProcess = scSim.CreateNewProcess("testProcess")
+    simulationTimeStep = macros.sec2nano(1.0)  # [ns]
+    testProcess.addTask(scSim.CreateNewTask("testTask", simulationTimeStep))
+
+    scSim.AddModelToTask("testTask", cModule)
+    scSim.AddModelToTask("testTask", dataRec)
+
+    graph = scSim.GetMessageConnectionGraph(includeUnlinked=False)
+    edgePairs = {(edge["sourceName"], edge["targetName"]) for edge in graph["edges"]}
+
+    assert ("dataOutMsg", "recordedMsg") in edgePairs
+
+
 def test_GetMessageConnectionGraph_with_input_message_recorder():
     """Check that input message recorders show their recorded input."""
     scSim = SimulationBaseClass.SimBaseClass()