cache TorBox CDN download URLs to reduce API call frequency

[mainLink0435]

📌 Description

• Caches TorBox CDN links for an amount of time to avoid calling the API every time and to help avoid API limits

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Target Branch Check (IMPORTANT)

• [ X] I confirm this PR is targeting the correct branch

Expected target:

• beta (for features)

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Changes Made

• fetchDownloadLink was building a ?redirect=true URL and storing that in the link cache. Because the redirect URL hits the TorBox API on every stream request, the cache was effectively decorative — every file access still incurred a full API round-trip and counted against rate limits.
• Removes redirect=true and instead resolves the real CDN URL at link-fetch time by decoding the JSON response. The CDN URL is then stored in the per-account link cache and reused for all stream requests until autoExpiresLinksAfter elapses.
• Also adds an expiry check in account.GetDownloadLink: ExpiresAt was already being set by all providers but was never enforced - the cache would serve stale links indefinitely until restart. The check ensures expired entries are re-fetched rather than returned.

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Testing

• [X ] Tested locally

Steps:

1. build dockerfile via gitea
2. ran in place of official build
3. additional debug logging confirmed CDN cache works as expected

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Risks / Notes

• the account.GetDownloadLink: ExpiresAt is actually being enforced across all providers.

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Screenshots (if applicable)

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Checklist

• [X ] Code builds successfully
• [ X] No console/log errors
• [ X] Reviewed my own code
• [ X] Target branch is correct