#1721: fetch issue comments count once per PR instead of once per review

[morphqdd]

Closes #1721.

judges/code-was-reviewed/code-was-reviewed.rb fetched Fbe.octo.issue_comments(repo, f.issue).count inside the reviews.each loop, once per review — but the result doesn't depend on the review at all (it's a property of the PR, not the individual review). For a PR with N new reviews in one judge cycle, this refetched the exact same issue-comments count N times instead of once, on top of the necessarily-per-review pull_request_review_comments call.

Fix: hoisted the fetch into a memoized count local (count ||= ...) computed once per PR, reused for every review's n.comments assignment. Fbe.if_absent's next if n.nil? guard still gates whether the fetch happens at all (already-recorded reviews skip it, same as before) — only the redundant repeat for multiple new reviews on the same PR is eliminated.

Added test_fetches_issue_comments_once_for_multiple_reviews, stubbing a PR with 2 new reviews and asserting the issues/60/comments endpoint is hit exactly once (assert_requested(..., times: 1)) instead of twice.

Note: I wasn't able to run the test suite locally due to an unrelated native-gem/Ruby-version mismatch in my environment (openssl gem compiled against a stale libruby). I verified the change via ruby -c (syntax OK) and rubocop (no new violations vs. the pre-existing baseline — confirmed by diffing rubocop output before/after on the unmodified file) and by tracing through the logic by hand.

[morphqdd]

@yegor256, please take a look when you have a moment.