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3007cb6f37
The ANN vector queries with all-zero vectors are allowed even on vector
indexes with similarity function set to cosine.
When enabling the rescoring option, those queries would fail as the rescoring
calls `similarity_cosine` function underneath, causing an `InvalidRequest` exception
as all-zero vectors were not allowed matching Cassandra's behaviour.
To eliminate the discrepancy we want the all-zero vector `similarity_cosine` calls to pass,
but return the NaN as the cosine similarity for zero vectors is mathematically incorrect.
We decided not to use arbitrary values contrary to USearch, for which the distance
(not to be confused with similarity) is defined as cos(0, 0) = 0, cos(0, x) = 1 while
supporting the range of values [0, 2].
If we wanted to convert that to similarity, that would mean sim_cos(0, x) = 0.5,
which does not support mathematical reasoning why that would be more similar than
for example vectors marking obtuse angles.
It's safe to assume that all-zero vectors for cosine similarity shouldn't make any impact,
therefore we return NaN and eliminate them from best results.
Adjusted the tests accordingly to check both proper Cassandra and Scylla's behaviour.
Fixes: SCYLLADB-456
(cherry picked from commit af0889d194)