ci: add pull-request checks, and make main pass them

[funcpp]

Groundwork for working through the contributions in #15.

What

Commit	Change
style: apply rustfmt to the workspace	Output of cargo fmt --all, no manual edits
fix: drop unneeded struct pattern on a unit variant	Statement::UnlockTables { .. } → Statement::UnlockTables
ci: run fmt, clippy, tests, and a Python smoke test on pull requests	New .github/workflows/ci.yml + README badge
ci: let dependabot track cargo dependencies	Adds the cargo ecosystem alongside github-actions

No behavior change.

Why

• No CI on pull requests. release.yml only triggers on version tags, so branches were unverified until release time.
• main was not rustfmt-clean — 19 hunks in build/expr.rs and resolve/mod.rs. Formatting noise leaks into unrelated diffs; fix: two column lineage correctness bugs (nondeterministic ordering, fabricated origins) #12 skipped cargo fmt for this reason and fix: harden column lineage resolution and performance #14 carries a reformat commit mid-stack.
• One clippy warning on main, which blocked running the gate with -D warnings.
• Dependabot watched Actions only, not sqlparser/pyo3/clap/serde.

Workflow

Four jobs on ubuntu-latest, on pull_request and pushes to main:

• rustfmt — cargo fmt --all --check
• clippy — --workspace --all-targets --all-features -- -D warnings
• test — cargo test --workspace --all-features
• python — maturin wheel build + the same smoke test as release.yml

clippy and test set up Python because sqllineage-python is a workspace member that links against libpython. Cross-platform and multi-version coverage stays in release.yml.

Verified locally

cargo fmt --all --check                                           exit 0
cargo clippy --workspace --all-targets --all-features -D warnings exit 0
cargo test --workspace --all-features                             exit 0  (88 tests + 1 doctest)
maturin build --manifest-path sqllineage-python/Cargo.toml        wheel built

Open

Cargo.lock is gitignored. Committing it would make CI reproducible for the shipped binary — separate call, not included here.

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