Deflake empty-block in mempool test

[masih]

TestMempoolProgressAfterCreateEmptyBlocksInterval used the same 5s value for CreateEmptyBlocksInterval and for the helper that requires the next event to arrive before timing out. After spending one full ensureTimeout asserting that no early block was produced, the test only gave the next empty block another ensureTimeout to be proposed, committed and published. On slower CI runners that boundary is tight enough for the helper to fire before the NewBlock event is delivered, even though consensus behavior is correct.

Fix that test by waiting for the exact next NewBlock height with the existing eventual helper. The test still asserts that no block is created during the full empty-block interval, and it now additionally checks that the next block is exactly the expected height.

Flaked in unrelated changes.

[github-actions]

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Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Mar 30, 2026, 6:37 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.74%. Comparing base (95ed1f5) to head (3cefaba).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3137   +/-   ##
=======================================
  Coverage   58.73%   58.74%           
=======================================
  Files        2095     2095           
  Lines      173517   173517           
=======================================
+ Hits       101920   101928    +8     
+ Misses      62481    62476    -5     
+ Partials     9116     9113    -3     

Flag	Coverage Δ
sei-chain-pr	68.61% <ø> (?)
sei-db	70.41% <ø> (ø)

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