Frame top and bottom row overexpanding

Hi there,

Thanks for your amazing library.
I just noticed something that looks a lot like a bug

root_container = Frame(Window(height=2, width=3))
layout = Layout(root_container)

app = Application(layout=layout)
app.run()

When I run this, I get this rendered to the screen:

┌─────────────────────────────────────────────────────────────────────────────────────────────────┐
│   │
│   │
└─────────────────────────────────────────────────────────────────────────────────────────────────┘

prompt_toolkit version: 3.0.31
python 3.10
Windows 10

Thanks!

Start by running the provided Python reproducer with Frame, Window, Layout, and Application.run to confirm the top and bottom rows expand beyond the requested 2x3 size. Trace the layout sizing from Window through Frame and Layout, then verify that the rendered output respects the requested dimensions.