refactor: simplify DNS discovery fallback

[xdustinface]

Use a tokio::time::Interval in the maintenance loop's select! instead of manual SystemTime elapsed tracking.
The interval arm is disabled in exclusive mode via a select guard and skips DNS if peers are already enough.

Also, the DNS lookup branch doesn't try to connect immediately but instead in the next loop cycle, which happens straight away.

Based on:

• fix: make use of stored peers #422

Summary by CodeRabbit

• Refactor
  • Simplified peer discovery mechanism: now uses periodic DNS refresh intervals instead of time-based tracking for network peer management.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PeerNetworkManager struct's DNS peer discovery mechanism was refactored to replace time-tracked, on-demand searches with a periodic timer-driven approach. A peer_search_started field was removed, and DNS discovery now runs at regular intervals via a dns_interval timer within the maintenance loop.

Changes

Cohort / File(s)	Summary
DNS Discovery Refactoring dash-spv/src/network/manager.rs	Removed peer_search_started: Arc<Mutex<Option<SystemTime>>> field and replaced time-based DNS delay tracking with periodic dns_interval timer mechanism. Updated struct initialization, Clone implementation, and maintenance loop logic to use interval-driven DNS discovery instead of start-time tracking.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Poem

🐰✨ The DNS search hops along with grace,
No need to track each starting place!
A timer ticks at intervals so true,
Discovery periodic—fresh and new!
One field removed, the maintenance glows bright,
Peer connections dancing through the night! 🌙

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: simplifying DNS discovery fallback logic by replacing manual SystemTime tracking with a periodic interval mechanism.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch refactor/peer-search-started

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No actionable comments were generated in the recent review. 🎉

🧹 Recent nitpick comments

dash-spv/src/network/manager.rs (1)

763-764: Use interval_at to defer the first DNS discovery probe by one interval period.

time::interval(DNS_DISCOVERY_DELAY) completes its first .tick() immediately, which would trigger DNS discovery on the very first maintenance loop iteration—potentially redundant with the immediate DNS discovery already performed in start() (lines 173–196). Defer the first tick by one period using interval_at:

Suggested change

-            let mut dns_interval = time::interval(DNS_DISCOVERY_DELAY);
+            let mut dns_interval =
+                time::interval_at(time::Instant::now() + DNS_DISCOVERY_DELAY, DNS_DISCOVERY_DELAY);

The is_connecting guard prevents duplicate connection attempts, so this is an efficiency improvement rather than a correctness issue.

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