[MRG] do not report untrusted jaccard ANI

[bluegenes]

fixes #2004

This PR modifies jaccardANIResult to only return an ANI value when the jaccard error does not exceed the recommended threshold. This means that ANI will not be returned to any jaccard ANI function (minhash, signature, compare, search, etc) if it is not trusted.

I haven't enabled forcibly returning ANI in minhash or signature because I still return the distance (so if you really want the untrustworthy ANI anyway, you can just do 1-distance).

[codecov]

Codecov Report

Merging #2011 (a06e43f) into latest (d425f6f) will increase coverage by 7.52%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           latest    #2011      +/-   ##
==========================================
+ Coverage   84.14%   91.67%   +7.52%     
==========================================
  Files         129       98      -31     
  Lines       15082    10807    -4275     
  Branches     2118     2119       +1     
==========================================
- Hits        12691     9907    -2784     
+ Misses       2095      604    -1491     
  Partials      296      296              

Flag	Coverage Δ
python	91.67% <100.00%> (+<0.01%)	⬆️
rust	?

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

Impacted Files	Coverage Δ
src/sourmash/search.py	97.89% <ø> (-0.01%)	⬇️
src/sourmash/distance_utils.py	99.35% <100.00%> (+0.02%)	⬆️
src/core/src/ffi/storage.rs
src/core/src/errors.rs
src/core/src/index/mod.rs
src/core/src/index/linear.rs
src/core/src/ffi/mod.rs
src/core/src/sketch/nodegraph.rs
src/core/src/ffi/index/mod.rs
src/core/src/ffi/cmd/compute.rs
... and 23 more

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[bluegenes]

ready for review @ctb @sourmash-bio/devs