feat(async search): add export async search docs method

[forshev]

Description

Add a new method to export documents found by async search

Fixes #472

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.14%. Comparing base (38bb573) to head (63c6e94).

Files with missing lines	Patch %	Lines
proxy/search/async.go	0.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #473      +/-   ##
==========================================
+ Coverage   71.11%   71.14%   +0.03%     
==========================================
  Files         232      232              
  Lines       18426    18466      +40     
==========================================
+ Hits        13103    13138      +35     
- Misses       4341     4345       +4     
- Partials      982      983       +1     

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[github-actions]

🔴 Performance Degradation

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Name	Previous	Current	Ratio	Verdict
Indexer-4	38bb57	251553
	686553494.00 B/op	765572502.00 B/op	1.12	🔴