chore: bump MSRV to Rust 1.95 and adopt new stable features

[acgetchell]

Closes #67

• Bump rust-version to 1.95 in Cargo.toml
• Bump channel to 1.95.0 in rust-toolchain.toml
• Add core::hint::cold_path() hints at cold/error branches:
  • src/exact.rs: validate_finite, validate_finite_vec, gauss_solve singular return, det_exact_f64 / solve_exact_f64 overflow returns, det_sign_exact Stage 2 Bareiss fallback
  • src/lu.rs: Lu::factor and Lu::solve_vec NonFinite / Singular returns
  • src/ldlt.rs: Ldlt::factor and Ldlt::solve_vec NonFinite / Singular returns
  • src/matrix.rs: det_direct D >= 5 fallback arm (legal because cold_path is const fn in 1.95) and det NonFinite / overflow scan
• Refactor det_sign_exact Stage 1 fast filter to use match + if let guard with let-chain, replacing the tuple destructure; semantics unchanged

Test results (local just ci):

• cargo fmt --all -- --check: clean
• cargo clippy --workspace --all-targets --all-features -D warnings -W clippy::pedantic -W clippy::nursery -W clippy::cargo: clean
• cargo test --features exact --lib: 258 passed, 0 failed
• cargo test --features exact (doctests + examples): 31 passed, 0 failed
• RUSTDOCFLAGS='-D warnings' cargo doc --no-deps --features exact: clean
• python tests: 101 passed

Summary by CodeRabbit

Chores

• Updated minimum required Rust toolchain version from 1.94 to 1.95.0. Users must upgrade their Rust installation before updating to this release.
• Implemented compiler-level performance optimizations on error handling and fallback paths across matrix operations to improve runtime efficiency when encountering invalid inputs or edge cases.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e194fdbd-0646-42ef-bab2-795018c530d5

📥 Commits

Reviewing files that changed from the base of the PR and between 0ab3c33 and f763b11.

📒 Files selected for processing (3)

• src/ldlt.rs
• src/lu.rs
• src/matrix.rs

📝 Walkthrough

Walkthrough

Bumped minimum Rust version from 1.94 to 1.95 across toolchain configuration. Added core::hint::cold_path() compiler hints to error-return and fallback paths in matrix determinant and linear solver implementations to optimize common-case execution.

Changes

Cohort / File(s)	Summary
Toolchain version bump Cargo.toml, rust-toolchain.toml	Updated MSRV from Rust 1.94 to 1.95 in both configuration files.
Cold-path hints in exact determinant/solver src/exact.rs	Added cold_path() calls on non-finite validation errors, refactored det_sign_exact Stage 1 from tuple destructuring to match with guard, unconditionally marked Bareiss fallback as cold path in Stage 2.
Cold-path hints in LU factorization/solve src/lu.rs	Added cold_path() import and calls on all error-return paths for non-finite pivot/multiplier/sum detection and singular pivot checks.
Cold-path hints in LDLT factorization/solve src/ldlt.rs	Added cold_path() calls immediately before non-finite and singular error returns during factorization and solve phases.
Cold-path hints in determinant computation src/matrix.rs	Added cold_path() calls in det_direct() D≥5 fallback arm and before non-finite element scanning in det().

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related issues

• Issue #67 directly describes this work: bumping MSRV to 1.95 and adopting core::hint::cold_path() for compiler hint optimization of error/fallback paths.

Possibly related PRs

• PR #73: Modifies src/exact.rs det_sign_exact control flow and Bareiss path, directly overlaps with this PR's refactoring of the same function.
• PR #34: Changes Matrix::det_direct behavior in src/matrix.rs, overlaps with this PR's det_direct cold-path additions.
• PR #45: Adjusts det_sign_exact usage of det_errbound() and related control flow, directly related to this PR's refactoring of Stage 1.

Suggested labels

rust, performance, enhancement, optimization

Poem

🐰 A hop and a skip to Rust forty-five!
Cold paths now whisper when errors arrive,
The hot path runs swift while exceptions freeze—
Determinants dance through optimization's breeze.
Cheers to the hints that help compilers see. 🎉

🚥 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 PR title accurately summarizes the main changes: bumping MSRV to Rust 1.95 and adopting new stable features (cold_path, if-let guards), which are the primary focus across all modified files.
Linked Issues check	✅ Passed	The PR successfully implements all core coding requirements from issue #67: bumped rust-version to 1.95, added cold_path() hints across exact/lu/ldlt/matrix modules on error paths and cold fallbacks, and refactored det_sign_exact Stage 1 with if-let guards.
Out of Scope Changes check	✅ Passed	All changes are within scope of issue #67: Cargo.toml/rust-toolchain.toml toolchain updates, cold_path() additions across specified modules, and det_sign_exact refactoring. No unrelated modifications are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chose/67-bump-msrv-1.95

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[codecov]

Codecov Report

❌ Patch coverage is 57.57576% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.58%. Comparing base (7f3d2e1) to head (f763b11).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ldlt.rs	0.00%	9 Missing ⚠️
src/lu.rs	66.66%	3 Missing ⚠️
src/exact.rs	90.90%	1 Missing ⚠️
src/matrix.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #91      +/-   ##
==========================================
- Coverage   90.26%   88.58%   -1.68%     
==========================================
  Files           5        5              
  Lines         452      482      +30     
==========================================
+ Hits          408      427      +19     
- Misses         44       55      +11     

Flag	Coverage Δ
unittests	88.58% <57.57%> (-1.68%)	⬇️

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