fix(raft): update NetBackoff::backoff() return type to Option<Backoff>

[polaz]

Summary

• openraft 0.10.0-alpha.18 changed NetBackoff trait: backoff() now returns Option<Backoff> instead of Backoff
• Both GrpcNetwork and StubNetwork impls updated to return Some(Backoff::new(...))
• Without this fix, coordinode-python CI fails when cargo resolves to alpha.18+ (Cargo.lock is gitignored in coordinode-embedded)

Closes #39

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 621759aa-15a6-4eb0-b526-3b7e4f1300c3

📥 Commits

Reviewing files that changed from the base of the PR and between 99a4e3a and 2983844.

📒 Files selected for processing (1)

• crates/coordinode-raft/src/cluster/network.rs

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📝 Walkthrough

Summary by CodeRabbit

• Refactor
  • Enhanced network retry mechanism to improve reliability and control flow clarity.

Walkthrough

The NetBackoff::backoff() trait method signature is updated to return Option<Backoff> instead of Backoff in both GrpcNetwork and StubNetwork implementations. Return values are wrapped in Some(...) to match the openraft 0.10.0-alpha.18+ API change.

Changes

NetBackoff Return Type Update

Layer / File(s)	Summary
Trait Implementation crates/coordinode-raft/src/cluster/network.rs	GrpcNetwork and StubNetwork backoff() methods now return Some(Backoff::new(...)) instead of Backoff directly, aligning with the openraft trait signature change.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: updating NetBackoff::backoff() return type to Option, which is the primary focus of this pull request.
Description check	✅ Passed	The description clearly explains the cause (openraft 0.10.0-alpha.18 trait change), the solution (wrapping return values in Some), and provides context on why this fix is necessary for CI.
Linked Issues check	✅ Passed	The pull request fully addresses issue #39 by updating both GrpcNetwork and StubNetwork implementations to return Option as required.
Out of Scope Changes check	✅ Passed	All changes are scoped to updating the NetBackoff trait implementations in crates/coordinode-raft/src/cluster/network.rs, directly addressing the requirements in issue #39.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/#39-netbackoff-option

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