Cask::Audit: reduce livecheck fetches

[samford]

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The existing livecheck-related cask audits can end up fetching the livecheck URL four times and this can cause problems if a server has sensitive rate limiting (e.g., Homebrew/homebrew-cask#241429 (comment)). This modifies the livecheck_version audit to cache the result that's also used in the hosting_with_livecheck and livecheck_https_availability audits. This will avoid a duplicate fetch and can avoid another if the livecheck URL uses HTTPS and the check doesn't fail. Most casks meet that criteria, so this should be a notable improvement.

There's still room for improvement, as the min_os audit calls cask_sparkle_min_os, which can also fetch the livecheck URL. It would be ideal if we could cache the livecheck content to avoid this duplicate fetch but I don't think that's possible with the current setup, so I'll have to revisit that later. [I have some in-progress work to add caching to livecheck and I may be able to leverage that in the future as a way of addressing this.]

[Copilot]

Pull request overview

This PR optimizes cask audit performance by reducing redundant livecheck URL fetches from up to three times down to one in most cases. This is achieved by introducing a caching mechanism for the livecheck version audit result.

• Adds @livecheck_result instance variable to cache livecheck audit results
• Modifies audit_livecheck_version to cache and reuse results across multiple audit methods
• Updates audit_hosting_with_livecheck to call audit_livecheck_version directly instead of accepting it as a parameter
• Adds early return optimization in audit_livecheck_https_availability to skip unnecessary checks when livecheck already uses HTTPS and succeeds

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[MikeMcQuaid]

Looks good once small nit addressed! Can self-merge without rereview.