[SVS] Add Tiered SVS index implementation

[rfsaliev]

Implemented Tiered version of Scalable Vector Search index (TieredSVSIndex)

• Vectors moved to backend in 1 background job as a bulk
• Add basic unit tests for SVS tiered index
• Add Python binding for SVS Tiered index
• Backend index synchronized for deleted vectors

Main objects this PR modified

1. New class TieredSVSIndex
2. Tiered factory modified to support TieredSVSIndex

• This PR introduces API changes
• This PR introduces serialization changes

TODO:

• Uncomment and fix unit tests copy-pasted from HNSW-tiered or remove if not relevant.

[codecov]

Codecov Report

Attention: Patch coverage is 95.76988% with 25 lines in your changes missing coverage. Please review.

Project coverage is 96.50%. Comparing base (ed35da4) to head (5e94154).

Files with missing lines	Patch %	Lines
src/VecSim/index_factories/tiered_factory.cpp	78.87%	15 Missing ⚠️
src/VecSim/index_factories/svs_factory.cpp	81.48%	5 Missing ⚠️
src/VecSim/algorithms/svs/svs_tiered.h	98.89%	4 Missing ⚠️
src/VecSim/algorithms/svs/svs_utils.h	98.63%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #631      +/-   ##
==========================================
+ Coverage   96.33%   96.50%   +0.16%     
==========================================
  Files         112      113       +1     
  Lines        6225     6785     +560     
==========================================
+ Hits         5997     6548     +551     
- Misses        228      237       +9     

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