fix(litestar): correctly handle sync context manager

[cofin]

Summary

Ensure the Litestar SQLSpecPlugin connection provider unwraps sync context managers before injecting connections.

Closes #238

The Problem

• SqliteConfig (and other sync adapters) return sync context managers from provide_connection()
• connection_provider_maker() treated any non-async context managers as ready-to-use connections, so Litestar stored _GeneratorContextManager objects.
• Requests failed with AttributeError: '_GeneratorContextManager' object has no attribute 'cursor' when the driver tried to call .cursor().

The Solution

• Wrap sync context managers with with_ensure_async_() so the provider always awaits the context manager path and stores the actual connection.
• Preserve the existing awaitable/object path for adapters that already return concrete connections.
• Add a regression test that exercises SqliteConfig to ensure sync context managers yield proper driver connections and clean up scope state.

Key Features

• Handles both async and sync connection context managers in connection_provider_maker().
• Reuses the shared sync-to-async helper instead of duplicating wrapper logic in the plugin.
• Adds a Litestar handler test confirming SqliteConfig requests receive real driver connections and scope cleanup occurs.