ANN tests: make the min_recall check strict

[achirkin]

In #1135, we adjusted the min_recall values to report if any regressions happen in ivf-pq. However, eval_neighbours function, which is used in several ANN test suites, doesn't fail unless the regression is really large (it prints a warning if the calculated recall is "slightly" smaller than the expected recall).
In this PR, I make eval_neighbours always fail if the calculated recall is smaller than the expected recall. Slightly adjust the tests and do a small refactoring along the way.

[achirkin]

NB: some of the affected algorithms are not deterministic due to concurrency etc.; I've successfully run the test suite on my workstation 35 times, but we should keep an eye on how it behaves on the CI machines as well.

[tfeher]

Thanks Artem for the PR! Indeed it is high time to enable tighter accuracy bounds. The PR looks good to me.

[codecov-commenter]

Codecov Report

Base: 87.99% // Head: 87.99% // No change to project coverage 👍

Coverage data is based on head (d317b6e) compared to base (0e96662).
Patch has no changes to coverable lines.

Additional details and impacted files

@@              Coverage Diff              @@
##           branch-23.02    #1156   +/-   ##
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  Coverage         87.99%   87.99%           
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  Files                21       21           
  Lines               483      483           
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  Hits                425      425           
  Misses               58       58           

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[cjnolet]

My recent merge commit broke the build. Just leaving a note here that I'll fix this.

[achirkin]

Did a dozen tests on a100 and v100, seems to be passing with the last adjustments.

[cjnolet]

/merge