perf(matrix): improve inf_norm throughput

[acgetchell]

• Check row-sum finiteness once per completed row on the success path.
• Replay only overflowing rows to preserve the first failing matrix coordinate.
• Preserve left-to-right accumulation and const evaluation across dimensions.

Closes #154

Summary by CodeRabbit

• Bug Fixes
  • Improved matrix norm error reporting by identifying the first column where an overflow or invalid value occurs.
  • Preserved left-to-right summation behavior for more predictable floating-point results.
  • Updated and expanded coverage for norm calculations involving overflow and rounding.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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Run ID: 13715094-5133-4a22-ab55-0c39f2977049

📥 Commits

Reviewing files that changed from the base of the PR and between 9292e32 and dc28f98.

📒 Files selected for processing (1)

• src/matrix.rs

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📝 Walkthrough

Walkthrough

Matrix::inf_norm now identifies the first column where a row’s prefix sum becomes non-finite. Tests update overflow-location expectations and verify that left-to-right summation order remains preserved.

Changes

Infinity-norm diagnostics

Layer / File(s)	Summary
Locate the first overflowing column src/matrix.rs	inf_norm replays absolute-value row summation left-to-right to report the first column causing a non-finite prefix sum.
Update infinity-norm validation src/matrix.rs	Overflow expectations are updated, and a regression test verifies left-to-right row-sum evaluation.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• acgetchell/la-stack#92: Updates Matrix::inf_norm handling and tests for non-finite row sums.
• acgetchell/la-stack#131: Modifies Matrix::inf_norm non-finite computation diagnostics.
• acgetchell/la-stack#133: Changes the finite-value construction used by Matrix::inf_norm.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Linked Issues check	❓ Inconclusive	The code matches the perf and error-semantics goals, but the provided context doesn't show the requested focused benchmarks across dimensions.	Add or link benchmark results for D=2,3,4,5,8,16,32,64 with before/after comparisons.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: improving Matrix::inf_norm performance.
Out of Scope Changes check	✅ Passed	The changes stay focused on Matrix::inf_norm and its tests, with no obvious unrelated scope creep.
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/154-inf-norm

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.83%. Comparing base (9292e32) to head (dc28f98).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #184      +/-   ##
==========================================
+ Coverage   97.81%   97.83%   +0.02%     
==========================================
  Files           8        8              
  Lines        4809     4859      +50     
==========================================
+ Hits         4704     4754      +50     
  Misses        105      105              

Flag	Coverage Δ
unittests	97.83% <100.00%> (+0.02%)	⬆️

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