perf(vector): improve dot and norm2_sq throughput

[acgetchell]

• Check accumulator finiteness once after the success-path reduction.
• Replay only non-finite reductions to preserve the first failing step.
• Preserve left-to-right fused accumulation and const evaluation.

Closes #155

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of non-finite results in dot-product and squared-norm calculations.
  • Error reporting now identifies the specific calculation step where an overflow or invalid result occurs.
  • Preserved left-to-right and fused calculation behavior for more consistent numerical results.

• Tests

  • Added coverage for overflow scenarios, intermediate failures, and expected numerical outcomes.

[coderabbitai]

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ℹ️ Recent review info

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Run ID: 8dffd343-f105-4984-92e7-76801792f23e

📥 Commits

Reviewing files that changed from the base of the PR and between df7a358 and ece54d7.

📒 Files selected for processing (1)

• src/vector.rs

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📝 Walkthrough

Walkthrough

Vector::dot now completes left-to-right FMA accumulation before checking finiteness. When overflow occurs, replay identifies the first failing index. Tests cover dot and squared-norm overflow provenance, const evaluation, accumulation ordering, and middle-step failures.

Changes

Vector overflow provenance

Layer / File(s)	Summary
Deferred accumulation and failure replay src/vector.rs	dot_with_operation defers non-finite detection until accumulation ends, while dot_non_finite_error replays FMA operations to report the first failing index.
Overflow and ordering validation src/vector.rs	Tests cover replayed overflow indices, const-evaluated errors, left-to-right FMA behavior, and failures occurring in middle accumulation steps.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• acgetchell/la-stack#133: Updates finiteness validation around vector dot and squared-norm operations.
• acgetchell/la-stack#135: Changes vector non-finite validation and failing-step reporting.
• acgetchell/la-stack#147: Adjusts finite handling for dot and squared-norm computations.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: improved throughput for Vector dot and norm2_sq operations.
Linked Issues check	✅ Passed	The changes address #155 by optimizing dot/norm2_sq behavior while preserving API, numerical behavior, and adding focused tests.
Out of Scope Changes check	✅ Passed	The PR stays scoped to vector kernel behavior and related tests, with no obvious unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch perf/155-vector-dot-norm2

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.87%. Comparing base (df7a358) to head (ece54d7).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
+ Coverage   97.81%   97.87%   +0.05%     
==========================================
  Files           8        8              
  Lines        4859     4944      +85     
==========================================
+ Hits         4753     4839      +86     
+ Misses        106      105       -1     

Flag	Coverage Δ
unittests	97.87% <100.00%> (+0.05%)	⬆️

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