Fix Flaky PebbleDB Test

[Kbhat1]

Describe your changes and provide context

• Fixes flaky test panic in pebbledb iterator w/ checks after SeekLT() operations before accessing Key() or Value()
• Previously SeekLT() failed and invalidated the iterator but code still accesses the iterator and potentially read garbage memory data
• reordered Close() to wait for the background snapshot goroutine to finish before closing streamHandler preventing race where the goroutine accesses a nil streamHandler.

Testing performed to validate your change

• Verified testing
• Running it to repro flakiness

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Nov 28, 2025, 7:11 PM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 39.88%. Comparing base (eed339b) to head (216ee58).
⚠️ Report is 523 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2571       +/-   ##
===========================================
- Coverage   43.09%   39.88%    -3.22%     
===========================================
  Files        1590       15     -1575     
  Lines      137470     1389   -136081     
===========================================
- Hits        59247      554    -58693     
+ Misses      72736      786    -71950     
+ Partials     5487       49     -5438     

Flag	Coverage Δ
sei-chain	?
sei-cosmos	?
sei-db	?
sei-tendermint	?
sei-wasmd	?
sei-wasmvm	39.88% <ø> (+0.22%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 1575 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[codecov]

Codecov Report

❌ Patch coverage is 10.22727% with 79 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.24%. Comparing base (b01060b) to head (316d350).

Files with missing lines	Patch %	Lines
sei-db/ss/test/storage_test_suite.go	0.00%	75 Missing ⚠️
sei-db/ss/pebbledb/iterator.go	33.33%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2571      +/-   ##
==========================================
- Coverage   44.19%   43.24%   -0.96%     
==========================================
  Files        1793     1447     -346     
  Lines      149498   115153   -34345     
==========================================
- Hits        66066    49793   -16273     
+ Misses      77549    61035   -16514     
+ Partials     5883     4325    -1558     

Flag	Coverage Δ
sei-chain	42.36% <ø> (ø)
sei-cosmos	40.15% <ø> (ø)
sei-db	44.74% <10.22%> (-0.19%)	⬇️
sei-ibc-go	56.39% <ø> (ø)
sei-tendermint	?
sei-wasmd	42.59% <ø> (ø)
sei-wasmvm	39.88% <ø> (ø)

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

Files with missing lines	Coverage Δ
sei-db/sc/memiavl/db.go	63.14% <100.00%> (-0.07%)	⬇️
sei-db/ss/pebbledb/iterator.go	52.72% <33.33%> (-1.48%)	⬇️
sei-db/ss/test/storage_test_suite.go	0.00% <0.00%> (ø)

... and 348 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[yzang2019]

Shall we add a specific failure scenario (instead of flaky test) to make sure iterator will return correctly when hitting this scenario in the future?