fix: ensure PeerDisconnected is emitted on write-path disconnects

[xdustinface]

This fixes flaky failures in some of the integration tests coming soon. When a peer disconnects and the write path (broken pipe) detects it before the read path (EOF), the PeerDisconnected event could be lost entirely. receive_message() returned
ConnectionFailed instead of PeerDisconnected, causing the reader loop to hit the catch-all error handler which slept 1 second before cleanup. During that sleep, the maintenance
loop could silently remove the peer from the pool, preventing the event from ever being emitted.

• Return PeerDisconnected from receive_message() when connection state is already cleared
• Remove unnecessary 1-second sleep in the reader loop error handler

Summary by CodeRabbit

• Bug Fixes
  • Improved network error handling and responsiveness by removing unnecessary delays and refining error classification in disconnect scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

Network peer error handling is refined by removing an unnecessary delay in the manager's error path and changing how missing internal reader state is reported in the peer module, aligning disconnection scenarios with a unified error type.

Changes

Cohort / File(s)	Summary
Network error handling dash-spv/src/network/manager.rs, dash-spv/src/network/peer.rs	Removed 1-second delay from peer reader error path; changed missing internal state error from ConnectionFailed to PeerDisconnected for consistency with EOF/disconnection handling.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A speedy dash through network lanes,
No more delays in error chains,
When readers fade, the state's now clear—
One voice for disconnection here,
Swift fixes make the protocol cheer!

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main fix: ensuring PeerDisconnected is emitted on write-path disconnects, which directly aligns with the root cause analysis and changes made.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into v0.42-dev

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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 fix/peer-reader-loop-race

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No actionable comments were generated in the recent review. 🎉

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