Cryptic panic when livereload server fails to start

There's a couple issues here that need to be fixed:

1. For some reason the hot reload port wasn't released, despite the application port being released. I'm not able to reproduce this behavior at the moment, so let's just keep an eye on it for now.

2. Nil pointer panic on *exe.Close

   panic: runtime error: invalid memory address or nil pointer dereference
   				panic: runtime error: invalid memory address or nil pointer dereference
   [signal SIGSEGV: segmentation violation code=0x1 addr=0xa0 pc=0x148aa70]
   
   goroutine 66 [running]:
   github.com/livebud/bud/package/exe.(*Cmd).Close(0x0)
   				/Users/m/dev/src/github.com/livebud/bud/package/exe/command.go:24 +0x70
   panic({0x151a1a0, 0x19de710})
   				/usr/local/go/src/runtime/panic.go:838 +0x207
   os/exec.(*Cmd).Wait(0x173cec0?)
   				/usr/local/go/src/os/exec/exec.go:499 +0x18
   github.com/livebud/bud/package/exe.(*Cmd).Wait(...)
   				/Users/m/dev/src/github.com/livebud/bud/package/exe/command.go:39
   github.com/livebud/bud/runtime/command/run.(*Command).startApp(0xc000256f60, {0x173cec0?, 0xc00024d300}, 0xc000243490)
   				/Users/m/dev/src/github.com/livebud/bud/runtime/command/run/run.go:115 +0x3c5
   github.com/livebud/bud/runtime/command/run.(*Command).Run.func2()
   				/Users/m/dev/src/github.com/livebud/bud/runtime/command/run/run.go:37 +0x29
   golang.org/x/sync/errgroup.(*Group).Go.func1()
   				/Users/m/dev/pkg/mod/golang.org/x/sync@v0.0.0-20220513210516-0976fa681c29/errgroup/errgroup.go:74 +0x64
   created by golang.org/x/sync/errgroup.(*Group).Go
   				/Users/m/dev/pkg/mod/golang.org/x/sync@v0.0.0-20220513210516-0976fa681c29/errgroup/errgroup.go:71 +0xa5
   

   The problem is that process is nil for some reason when calling the following: https://github.com/livebud/bud/blob/63900d258ae92faa4faf14e834021347f202d8a1/runtime/command/run/run.go#L75

3. Need a better error for unable to start the live reload server. Perhaps:

   fmt.Errorf("Error starting the live reload server on %s: %w", address, err)
   

   Eventually, I'd like to find a free port and propagate the change accordingly, but for now, I think we just supply a better error.

Steps to reproduce

1. This can be reproduced by altering the following:

https://github.com/livebud/bud/blob/63900d258ae92faa4faf14e834021347f202d8a1/runtime/command/run/run.go#L117-L120

func (c *Command) startHot(ctx context.Context, hotServer *hot.Server) error {
	// TODO: host should be dynamic
+	return fmt.Errorf("failed to listen")
-	return hotServer.ListenAndServe(ctx, "127.0.0.1:35729")
}

2. Within the bud repository, call go run main.go -C examples/hn run