MB-71216, MB-71650: Implement fast merge over binary index classes

[Thejas-bhat]

• This change also comes with bug fixes in cases where we fail to create a centroid index, but the application decides to fallback to the naive merge algorithm instead of fast merge
• Brings in these fixes in zapx/v17:
  • b7d79e6 Abhi Dangeti, Likith B | Address panic observed while operating with file callbacks (Address panic observed while operating with file callbacks zapx#404)
  • b4e42c5 Thejas-bhat | MB-71216: implement fast merge for binary index class (MB-71216: implement fast merge for binary index class zapx#393)
  • ca1c2cf Thejas-bhat | make the faissIndex interface and implementation more modular (make the faissIndex interface and implementation more modular zapx#403)
  • f330de0 Likith B | Process In-Memory Segment Bases Before Persisting (Process In-Memory Segment Bases Before Persisting zapx#402)
  • 3468d01 Likith B | MB-71216: Added Support for IVFRaBitQ Indexes (MB-71216: Added Support for IVFRaBitQ Indexes zapx#391)

[coveralls]

coverage: 51.851% (+0.02%) from 51.835% — fastbivf into master