Change IDF formula

[lmores]

Implement the change being discussed in #1140.

Also directly import numpy.log to avoid attribute access inside for loop.

[codecov]

Codecov Report

Base: 73.84% // Head: 73.84% // No change to project coverage 👍

Coverage data is based on head (335adc7) compared to base (baa6071).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1141   +/-   ##
=======================================
  Coverage   73.84%   73.84%           
=======================================
  Files          28       28           
  Lines        2294     2294           
=======================================
  Hits         1694     1694           
  Misses        600      600           

Impacted Files	Coverage Δ
dedupe/canopy_index.py	100.00% <100.00%> (ø)

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[lmores]

Experimental verification required.

[fgregg]

@benchmark

[github-actions]

(logs)

[fgregg]

it looks like it did maybe improve precision and recall for the restaurant dataset. why don't you re-open this and i can take a look at some other datasets.