Expose multihop_search in wrapped_async.rs

[hakashya]

• Does this PR have a descriptive title that could go in our release notes?
• Does this PR add any new dependencies?
• Does this PR modify any existing APIs?
• Is the change to the API backwards compatible?
• Should this result in any changes to our documentation, either updating existing docs or adding new ones?

Reference Issues/PRs

What does this implement/fix? Briefly explain your changes.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.44%. Comparing base (1016934) to head (223d290).

Files with missing lines	Patch %	Lines
diskann-providers/src/index/wrapped_async.rs	0.00%	17 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #815      +/-   ##
==========================================
- Coverage   89.46%   89.44%   -0.02%     
==========================================
  Files         432      432              
  Lines       79629    79646      +17     
==========================================
  Hits        71238    71238              
- Misses       8391     8408      +17     

Flag	Coverage Δ
miri	89.44% <0.00%> (-0.02%)	⬇️
unittests	89.29% <0.00%> (-0.02%)	⬇️

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Files with missing lines	Coverage Δ
diskann-providers/src/index/wrapped_async.rs	0.00% <0.00%> (ø)

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