[MOD-13347] Add SQ8 type support to GetDistFunc template

[meiravgri]

This PR generalizes the GetDistFunc template to support comparing vectors of different types.

Changes

• Extended GetDistFunc template signature from <DataType, DistType> to <VecType1, DistType, VecType2 = VecType1>, where VecType2 defaults to VecType1 for symmetric comparisons
• Introduced vecsim_types::sq8 type to represent scalar-quantized 8-bit vectors
• Added GetDistFunc specializations for SQ8:
  • Symmetric: GetDistFunc<sq8, float> → SQ8-to-SQ8 distance functions
  • Asymmetric: GetDistFunc<sq8, float, float> → SQ8-to-float distance functions
• Added unit tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.15%. Comparing base (997ca70) to head (6cbabd1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #880      +/-   ##
==========================================
+ Coverage   97.04%   97.15%   +0.11%     
==========================================
  Files         128      128              
  Lines        7586     7604      +18     
==========================================
+ Hits         7362     7388      +26     
+ Misses        224      216       -8     

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