DBSCAN utilize rbc eps_neighbors

[mfoerste4]

This PR enables rbc eps-neighbor computation via raft. The resulting adjacency matrix is sparse and allows to skip the implicit conversion.

Notes:

• the 'algorithm'-parameter was added to the DBSCAN init signature to allow the user to choose (default is 'brute', 'rbc' is optional)
• the memory management is still very conservative, assuming a dense adjacency matrix and therefore selecting comparably small batches
• in case maximum row length of a batch is sufficiently small the CSR structure can be computed in a single pass

CC @tfeher

[mfoerste4]

rerun tests

[mfoerste4]

@tfeher , thanks for reviewing. I just added a small correction and re-triggered the CI.

[mfoerste4]

/test

[mfoerste4]

rerun tests

[dantegd]

/merge