Added capability to modify the step size.

ModeliRpc.proto

@@ -38,6 +38,9 @@ service ModeliBackend {
     rpc NewValues (NewValuesRequest) returns (stream NewValuesResponse);
     // Stream log messages to the client
     rpc Log (LogRequest) returns (stream LogResponse);
+
+    // Modify the simulation step size
+    rpc SetStepSize (SetStepSizeRequest) returns (SetStepSizeResponse);
 }
 
 // The metadata of a ChannelLink
@@ -183,3 +186,9 @@ message LogResponse {
     int32 status = 2;
     string message = 3;
 }
+
+message SetStepSizeRequest {
+    double step_size = 1;
+}
+
+message SetStepSizeResponse {}
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