Add per-direction cluster link established counter info fields

[enjoy-binbin]

Expose two new CLUSTER INFO counters to track cluster link:

• total_cluster_links_established_inbound: inbound links
  successfully established with peers via accept
• total_cluster_links_established_outbound: outbound links
  successfully established to peers via connect

Unlike the existing topology-derived cluster_connections field,
these are precise cumulative counters incremented when a link
is actually established (on accept, and on successful connect).
They help surface network flapping / frequent re-connections
between nodes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: b97cf894-fbec-47f9-9173-9eafdd36cb7c

📥 Commits

Reviewing files that changed from the base of the PR and between b2cf989 and e195918.

📒 Files selected for processing (1)

• tests/unit/cluster/info.tcl

🚧 Files skipped from review as they are similar to previous changes (1)

• tests/unit/cluster/info.tcl

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📝 Walkthrough

Walkthrough

Cluster link statistics now count successfully established inbound and outbound connections, expose both totals in cluster info, reset them with cluster statistics, and validate startup and reset behavior in unit tests.

Changes

Cluster Link Statistics

Layer / File(s)	Summary
Track and report established links src/cluster_legacy.h, src/cluster_legacy.c	Adds inbound and outbound counters, increments them when links are accepted or connected, and exposes their totals through cluster info.
Reset and validate counters src/cluster.c, tests/unit/cluster/info.tcl	Resets both counters through CONFIG RESETSTAT and verifies startup thresholds plus post-reset zero values.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant ClusterPeer
  participant ClusterHandlers
  participant clusterState
  participant ClusterInfo
  ClusterPeer->>ClusterHandlers: establish inbound or outbound link
  ClusterHandlers->>clusterState: increment corresponding counter
  ClusterInfo->>clusterState: read establishment totals
  clusterState-->>ClusterInfo: inbound and outbound totals

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the new per-direction cluster link established counters added to CLUSTER INFO.
Description check	✅ Passed	The description directly matches the changes by explaining the new inbound and outbound cluster link counters and their purpose.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tests/unit/cluster/info.tcl`:
- Around line 64-65: Update the second assertion in the cluster link checks to
validate node 2’s inbound counter instead of repeating
total_cluster_links_established_outbound, while preserving the existing
threshold and outbound assertion.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 9e99d1ea-5519-4a6d-8e33-33dddc0e2fd4

📥 Commits

Reviewing files that changed from the base of the PR and between 050b065 and b2cf989.

📒 Files selected for processing (4)

• src/cluster.c
• src/cluster_legacy.c
• src/cluster_legacy.h
• tests/unit/cluster/info.tcl

[valkey-review-bot]

Implementation looks correct — counters increment only after the connection-state checks in both handlers, and reset/init via resetClusterStats() is covered. One copy-paste issue in the new test.