fix: use ASGIConnection instead of Request for flash

[cofin]

Description

Currently, the FlashPlugin expects the request parameter to be a type of Request. However, there's no reason it can't use the parent class ASGIConnection.

Doing this, allows for flash to be called in guards that expect an ASGIConnection instead of Request:

def requires_active_user(connection: ASGIConnection, _: BaseRouteHandler) -> None:
    if connection.user.is_active:
        return
    msg = "Your user account is inactive."
    flash(connection, msg, category="error")
    raise PermissionDeniedException(msg)

Closes

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/3626