chore: configure crates.io publishing, CI, and Codecov

[philippemnoel]

Sets superkmeans-rs up for release to crates.io and continuous integration, mirroring the paradedb/decimal-bytes setup and adapting it to this crate's BLAS feature model.

What's included

Packaging & docs

• Cargo.toml: publishing metadata — authors, repository, homepage, readme, categories, keywords, and rust-version = "1.85" (MSRV, matching edition 2024).
• README.md: overview, quick-start usage, BLAS-backend matrix, and status badges (crates.io, Codecov, CI, docs.rs, license).
• LICENSE (MIT) and CONTRIBUTING.md.

CI — .github/workflows/ci.yml

• test: matrix of default features (Linux), openblas (Linux, installs libopenblas-dev), and accelerate (macOS).
• clippy (default + openblas), fmt, docs (RUSTDOCFLAGS=-D warnings), msrv (checks against Rust 1.85), and coverage (uploads lcov to Codecov, slug paradedb/superkmeans-rs).
• Note: unlike decimal-bytes, this does not use --all-features. accelerate (a macOS-only framework) and openblas (a system lib) are mutually exclusive and platform-specific, so enabling both at once fails to link. The matrix exercises each backend on a platform where it works.

Release — .github/workflows/release.yml

• Tag-driven (v*): validate (tag == Cargo.toml version, tests, clippy) → cargo publish → GitHub release.

Dependabot — .github/dependabot.yml

• Monthly cargo and github-actions updates.

Source changes to satisfy the new CI gates

• rustfmt normalization (src/pdxearch.rs signature wrapping).
• Two Clippy autofixes: div_ceil (src/utils.rs), is_multiple_of (src/layout.rs) — both semantics-preserving.
• A doc-comment blank line in build.rs.
• Crate-wide #[allow(...)] in src/lib.rs for the stylistic lints the numeric kernels intentionally trip (needless_range_loop, too_many_arguments, manual_memcpy, field_reassign_with_default, doc_lazy_continuation) — rather than reshaping the ports of the C++ kernels.

Verified locally (Rust 1.94)

cargo fmt --check, cargo clippy -- -D warnings (default and --features openblas), cargo doc, cargo test (16 pass), and cargo publish --dry-run (packages 27 files) all pass.

Required before release / green coverage

Two repo secrets must be configured in Settings → Secrets and variables → Actions:

• CARGO_REGISTRY_TOKEN — crates.io publish token (release workflow).
• CODECOV_TOKEN — Codecov upload token (coverage job; it currently runs with fail_ci_if_error: true).

Also confirm the crate name superkmeans-rs is available/owned on crates.io before the first v0.1.0 tag.

🤖 Generated with Claude Code

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Generated by Claude Code

[codecov]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

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