[MRG] Adjust Index.find search protocol to support selective collection of matches

[ctb]

This PR builds off of the new Index.find method and JaccardSearch protocol in #1392 to provide selective collection of matches.

In #1392, we introduced the following logic in Index.find(...):

            score = search_fn.score_fn(...)

            if search_fn.passes(score):                                     
                search_fn.collect(score)
                yield subj, score

and this PR changes the collect(...) method so that it takes the match and can decide whether or not to continue:

            score = search_fn.score_fn(...)

            if search_fn.passes(score):                                     
                if search_fn.collect(score, subj):
                    yield subj, score

This permits the collect(...) method on JaccardSearch objects to inspect the potential match and potentially decide to reject it. In turn, this enables signature "masking" functionality potentially useful for #849 and #985.

Ref #1392 (comment)

cc @bluegenes

[codecov]

Codecov Report

Merging #1477 (5309bcb) into latest (f02e250) will increase coverage by 5.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           latest    #1477      +/-   ##
==========================================
+ Coverage   89.71%   94.89%   +5.17%     
==========================================
  Files         123       96      -27     
  Lines       19464    15926    -3538     
  Branches     1483     1497      +14     
==========================================
- Hits        17463    15113    -2350     
+ Misses       1775      587    -1188     
  Partials      226      226              

Flag	Coverage Δ
python	94.89% <100.00%> (+0.02%)	⬆️
rust	?

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

Impacted Files	Coverage Δ
src/sourmash/index.py	94.62% <100.00%> (ø)
src/sourmash/lca/lca_db.py	92.30% <100.00%> (ø)
src/sourmash/sbt.py	80.85% <100.00%> (+0.02%)	⬆️
src/sourmash/search.py	93.26% <100.00%> (+0.03%)	⬆️
tests/test_index.py	100.00% <100.00%> (ø)
tests/test_search.py	98.48% <100.00%> (ø)
src/core/src/ffi/utils.rs
src/core/src/index/sbt/mhbt.rs
src/core/src/index/linear.rs
src/core/src/sketch/nodegraph.rs
... and 23 more

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[ctb]

@bluegenes I think this is ready for review.

[bluegenes]

As preliminary functionality, this looks good to me!