fix: Handle TimeoutError in fetch_info to prevent double wait

[arabcoders]

This pull request introduces two main improvements: (1) URL validation is now performed asynchronously in a thread to avoid blocking the event loop, and (2) extraction timeouts are dynamically increased ("budgeted") for requests that are expected to involve significant sleep intervals, improving reliability for sleep-heavy sources. The changes also include new tests to ensure these behaviors are correct.

Asynchronous URL Validation:

• All usages of validate_url in request handlers are now run using asyncio.to_thread, ensuring that potentially blocking validation does not block the main event loop.

Timeout Budgeting for Sleep-Heavy Extraction:

• A new budget_sleep parameter is added to fetch_info and all its intended call sites. When enabled, the extraction timeout is increased based on the configured sleep interval, up to a maximum of 300 seconds extra. This helps prevent premature timeouts for sources that require many sleep intervals.

Other Improvements:

• In app/routes/api/images.py, the thumbnail fetcher now explicitly sets a 10-second timeout for HTTP requests.