1994 Subaru Justy Idling

By "coasting" I'm going to presume you mean the car is rolling but not being driven by the engine.

If you keep it in gear while doing this, you'll be keeping the engine RPMs above idle. To be honest, idle is the most fuel inefficient engine speed there is. If you're "coasting" for any distance and able to keep rolling before "providing motivation to close the gap" I would shut it off, like NASCAR drivers do under cautions. Admittedly, your little engine isn't consuming as much fuel as theirs. That said, 54 MPG is pretty awesome.

As long as the engine is running, there's fuel going to the engine, even with a fuel injected engine.

With a carbureted engine, it's your foot that controls fuel flow to the engine. The fuel pump only sends fuel to the carburetor when the float bowl level drops below a certain level, whether the engine is running at full speed, or you're just starting up, or idling. When you depress the gas pedal (in a fuel injected vehicle it's an accelerator pedal because it control air flow to the engine and throttle body), the linkage on the carb causes an accelerator pump to be pushed. This sends an extra shot of fuel to the engine to help accelerate the vehicle.