MNT Transitional changes in prep for v0.30

[VarIr]

Some major changes in preparation for v0.30, including

• Remove legacy neighbors code. From v0.30 skhubness lives side-by-side with sklearn, instead of hacking their classes.
• Remove old-style Hubness estimation which relied on hacked sklearn NearestNeighbors.
• Remove many unnecessary tests at the cost of potentially also removing some useful tests. The plethora of tests essentially copied over from sklearn had become too large a burden for this transition. Useful tests will be reintroduced at a later time. While risky, without this, the transition might never happen.
• Multiple small adaptation in tests (e.g., dealing with renamed sklearn functions).
• Github Actions badge in readme
• Remove falconn requirement
• Remove setup.py

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (main@45adfbc). Click here to learn what that means. The diff coverage is n/a.

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[lgtm-com[bot]]

This pull request fixes 10 alerts when merging e0ed281810fbad2616eeb2be5f356d123109cb7e into 45adfbc47897021d8ce93fc216d03f2aaf1b124d - view on LGTM.com

fixed alerts:

• 5 for Conflicting attributes in base classes
• 3 for Unused import
• 2 for Implicit string concatenation in a list