Deflake async peer registration and harden PeerList.All

[masih]

TestReactor_BlockProviders flakes because peer connectivity is established before the reactor has asynchronously processed peer-updates and appended all peers to r.peers.

Fix this categorically by:

• waiting in reactorTestSuite.AddPeer until the new peer is visible in reactor.peers before returning;
• making PeerList.All() return a copy (snapshot) instead of the internal slice;
• adding TestPeerListAllReturnsSnapshot to enforce snapshot semantics.

This removes timing-sensitive reads of partially-registered peers and prevents callers from observing/mutating shared peer-list backing storage.

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Mar 5, 2026, 12:10 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.21%. Comparing base (0fea76f) to head (4484665).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2999      +/-   ##
==========================================
- Coverage   58.40%   58.21%   -0.20%     
==========================================
  Files        2110     2112       +2     
  Lines      175009   173397    -1612     
==========================================
- Hits       102213   100942    -1271     
+ Misses      63767    63456     -311     
+ Partials     9029     8999      -30     

Flag	Coverage Δ
sei-chain-pr	73.21% <100.00%> (?)
sei-db	70.41% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-tendermint/internal/statesync/dispatcher.go	79.68% <100.00%> (+5.87%)	⬆️

... and 79 files with indirect coverage changes

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