fix: repair dead discussion mentor-counting branch

[kaizeenn]

Description

Fixes #774.

Three layered defects made enable_mentor_count a complete no-op (or a crash) for GitHub Discussions:

1. GraphQL fetched no comment author data

discussions.py queried comments(first: 1) { nodes { createdAt } } — no author field, and only 1 comment. Expanded to comments(first: 100) with author { login __typename } on each comment node. Added author { login __typename } to the discussion node itself so the opener's login is available for the self-comment filter.

2. Attribute access on dict nodes would AttributeError

most_active_mentors.py used comment.user.login, comment.submitted_at, comment.ready_for_review_at on plain GraphQL dicts. Replaced with comment.get('author') or {} dict access throughout.

3. Self-reference in ignore_comment

The old code passed comment.user as both issue_user and comment_user, so the guard comment_user.login == issue_user.login always fired and every comment was skipped. Fixed by threading discussion['author']['login'] as the discussion-author login and comparing directly, without going through ignore_comment (which expects github3 objects, not dicts).

Structural fix

Moved the discussion block outside the if issue: guard so it actually runs when the call-site passes issue=None, discussion=<dict> (as issue_metrics.py does).

Development notes

Changed files: discussions.py, most_active_mentors.py, test_most_active_mentors.py.

Added TestCountCommentsDiscussions with 7 cases:

• basic count
• author self-comment is ignored
• bot commenter is ignored
• ignore_users respected
• multiple distinct commenters
• empty comments list
• null author (deleted account) handled gracefully

pytest test_most_active_mentors.py — 11 passed (4 baseline + 7 new). Commit signed off (DCO).