Optimize push rule file size check using quarantine dir

What does this MR do and why?

Related to: Improve performance for maximum file size push ... (#505364 - closed)

This MR optimizes the file size limit check process for push rules by using the quarantine directory.

The previous implementation required a full graph traversal, which was inefficient. Checking only the quarantine directory significantly improves performance while maintaining accuracy. Since this is an EE-only feature, a new class EE::Gitlab::Checks::PushRules::FileSizeCheck has been introduced to retrieve the push rule file size limit.

The existing approach should be removed when cleaning up the push_rule_file_size_limit feature flag.

MR acceptance checklist

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Screenshots or screen recordings

Local test with the FF on

How to set up and validate locally

1.Set a push rule file size limit in the project settings. (settings -> Repository -> Push rules)

2.Try pushing a file larger than the limit – it should be rejected.

3.Try pushing a file within the limit – it should succeed.