[BUG] Toasts don't show after redirect

[vacmar01]

Describe the bug
When adding a toast and then redirecting to a new route (either through RedirectResponse or HttpHeader('HX-Redirect') it doesn't show up after the redirect. The session is empty after the redirect (at least the key for the toasts).

Minimal Reproducible Example

from fasthtml.common import *

app, rt = fast_app(live=True, debug=True)

setup_toasts(app)

@rt('/')
def get(): 
    return Div(
        H1('Hello, World!'),
        P('This is a simple example of a FastAPI app using FastHTML.'),
        Form(
            Input(
                type='text',
                placeholder='Enter your name',
                name='name',
            ),
            Button('Submit', type='submit'),
            method='post',
            action='/result',
        ),
        cls='container',
        style='max-width: 680px',
    )
    
@rt('/result')
def post(name: str, session): 
    add_toast(session, f'Hello, {name}!')
    print(session)
    return RedirectResponse('/result', status_code=303)
    

@rt('/result')
def get(_, session):
    print("session after redirect: ", session) 
    return Div(
        H1('Hello, World!'),
        P('This is a simple example of a FastAPI app using FastHTML.'),
        cls='container',
        style='max-width: 680px',
    )
    
serve()

Expected behavior
I would expect the toasts to show up, even after redirecting. A possible scenario in a real-life app would be to show the user that they are now logged in.

Environment Information
Please provide the following version information:

• fastlite version: 0.0.9
• fastcore version: 1.7.1
• fasthtml version: 0.4.4

Confirmation
Please confirm the following:

• I have read the FAQ (https://docs.fastht.ml/explains/faq.html)
• I have provided a minimal reproducible example
• I have included the versions of fastlite, fastcore, and fasthtml
• I understand that this is a volunteer open source project with no commercial support.

Additional context
Add any other context about the problem here.

Screenshots
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