fix FP16 tests precision overflow [MOD-13429]

[dor-forer]

Describe the changes in the pull request

This PR fixes FP16 SVS tests' precision and assertion issues:

• Fix FP16 overflow in batch iterator tests: Scale vector indices by 0.1 to avoid FP16 overflow in L2 distance calculations.
• Changed the ARM machine include the SVE optimizations

Tests updated:
'test_batch_iterator'
test_override
test_batch_iterator_basic

Which issues this PR fixes

1. MOD-13429

Main objects this PR modified

1. ...
2. ...

Mark if applicable

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

[Copilot]

Pull request overview

This PR addresses FP16 precision overflow issues in vector similarity search tests by introducing scale factors to prevent distance calculations from exceeding FP16's maximum value (~65504). The changes ensure test vectors remain within safe numerical ranges while preserving test correctness.

Key changes:

• Added scale factor (0.1f) to SVS tiered index batch iterator tests to prevent overflow when n=1000
• Added scale factor (0.01f) to FP16 override and batch iterator tests to prevent overflow when n=250
• Upgraded ARM CI infrastructure from t4g.medium to r8g.xlarge for better performance

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
tests/unit/test_svs_fp16.cpp	Introduced 0.1f scale factor to prevent FP16 overflow in tiered batch iterator tests with proper documentation
tests/unit/test_fp16.cpp	Added 0.01f scale factor to test_override and test_batch_iterator_basic, plus tolerance-based comparison for FP16 precision loss
.github/workflows/arm.yml	Upgraded EC2 instance type to r8g.xlarge for improved CI performance

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.13%. Comparing base (f6df960) to head (39ce274).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #884   +/-   ##
=======================================
  Coverage   97.13%   97.13%           
=======================================
  Files         129      129           
  Lines        7614     7615    +1     
=======================================
+ Hits         7396     7397    +1     
  Misses        218      218           

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[meiravgri]

Are the tests in the description relevant?

[dor-forer]

@meiravgri Sorry it was an old description