docs: Add comprehensive meta-review of open PRs with clickable links

[Copilot]

Overview

Created systematic review of 55 open PRs to identify merge candidates, dependencies, and stale items. Document organizes PRs by readiness and semantic relationships. All PR references use clickable GitHub links for easy navigation.

Changes

• PR_REVIEW.md (621 lines): Comprehensive analysis organizing PRs into actionable categories
• PR References: All PR references converted to clickable markdown links (e.g., [#2515](https://github.com/igraph/rigraph/pull/2515))

Key Findings

Immediate Actions

• 2 PRs ready to merge (#2515 clean, #2513 needs CI)
• 1 major PR needs urgent review (#2485: autogenerate 108 functions)

Critical Conflicts

• Parameter naming: #2458 vs #2450 contradict each other (vids vs vertices)
• Resolution required before either can merge

Semantic Groupings

Identified 7 PR groups with interdependencies:

1. Parameter naming (4 PRs) - resolve conflict first
2. igraph 0.10 graph constructors (5 PRs) - review together for consistency
3. igraph 0.10 other functions (5 PRs) - can merge independently
4. Breaking changes (6+ PRs) - bundle for next major release
5. Bug fixes (4 PRs) - low risk, prioritize
6. Infrastructure (4 PRs) - may have dependencies
7. Documentation (3 PRs) - independent

Stale Items

• 5 PRs from 2023-2024 (oldest: 33 months) - recommend closure or rebase
• 2 PRs explicitly blocked - resolve blockers

Document Structure

• Executive summary with status overview and key observations
• PRs categorized by priority and readiness
• Dependency map showing semantic relationships
• Actionable recommendations with timeline
• Statistics by type, age, author, status

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• By submitting this pull request, I assign the copyright of my contribution to The igraph development team.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Meta-review: order open PRs</issue_title>
<issue_description>We have many open PRs and lost track. Which can be merged easily, which are dependent of each other semantically, which need more work? Create a list in a Markdown file.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Meta-review: order open PRs #2523

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[krlmlr]

@copilot: Use clickable links instead of # for PRs.

[Copilot]

@copilot: Use clickable links instead of # for PRs.

Done in 7e1e804. All PR references now use clickable links to GitHub.