fix(async search): skip missing fracs

[forshev]

Description

Skip evicted fracs in async search

---

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[github-actions]

🔴 Performance Degradation

Some benchmarks have degraded compared to the previous run.
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Name	Previous	Current	Ratio	Verdict
GenerateDocs-4	6ae568	044fcb
	957.90 ns/op	1132.00 ns/op	1.18	🔴
MutexListAppend-4	6ae568	044fcb
	184.44 MB/s	166.21 MB/s	0.90	🔴

[codecov-commenter]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.46%. Comparing base (6ae5683) to head (5d17d99).

Files with missing lines	Patch %	Lines
asyncsearcher/async_searcher.go	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #343      +/-   ##
==========================================
- Coverage   71.49%   71.46%   -0.04%     
==========================================
  Files         204      204              
  Lines       14857    14860       +3     
==========================================
- Hits        10622    10619       -3     
- Misses       3471     3476       +5     
- Partials      764      765       +1     

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