ci(test): add lance-graph-contract unit tests to the test gate

[AdaWorldAPI]

Summary

Closes the gap that let PR #322's log_norm_growth_negative_when_m_attenuates ship green and sit red on main for almost a day.

The Style Check / clippy job already type-checks crates/lance-graph-contract --lib --tests, but clippy does not execute tests — it just compiles them. So a logically-broken assertion compiles green, ships, and is caught only after merge.

PR #322 hit exactly this trap. Its log_norm_growth_negative_when_m_attenuates asserted that an attenuating M with seed = I produces NEGATIVE log-norm growth, but ‖log(propagated)‖²_F is structurally non-negative for any non-identity propagated, so the assertion was unsatisfiable from the start. Clippy passed, the PR shipped, and the regression sat red on every subsequent PR until PR #326 fixes the test body.

Fix

Add one step to the existing test job in rust-test.yml:

- name: Run contract unit tests
  run: cargo test --manifest-path crates/lance-graph-contract/Cargo.toml --lib

It rides on the existing job's setup — same toolchain, same Swatinem cache, same protobuf-compiler install — so the marginal cost is just the build (~1 s, zero-dep crate per CLAUDE.md) plus test execution (sub-second, 350 logic-only tests).

Cost / blast radius

• 11 lines of YAML.
• One additional ~2 s step in the existing test (stable) job. No new job, no new runner, no new cache.
• Catches contract-crate test regressions before merge instead of after.

Sequencing

⚠ This PR depends on PR #326 landing first. If it lands before #326, the new step turns CI red on main, because PR #322's broken test is still on main today (349 passed; 1 failed). Recommended merge order:

1. Merge PR fix(sigma-propagation): use non-identity seed in log_norm_growth_negative test #326 (test-body fix) → main becomes 350/350 green.
2. Merge this PR → CI gate locks the green state in place.

If preferred, this can also be rebased on top of #326 directly, but keeping them separate makes the intent clear: #326 = correctness fix, #327 (the rustfmt drift) = style fix, this = process fix.

What this PR does NOT do

• Does NOT add a coverage gate — test-with-coverage already runs against lance-graph only; widening coverage to the contract crate is a follow-up.
• Does NOT add doc-test coverage for the contract crate — the contract crate has few doc-tests today; if we want them gated, that's a separate one-line addition.
• Does NOT touch any other crate's CI surface. cognitive-shader-driver, lance-graph-callcenter, lance-graph-planner are still un-test-gated by CI; bringing them in is a separate scoping decision (some have heavier dep trees that would cost real CI time).

Companion PRs

• PR fix(sigma-propagation): use non-identity seed in log_norm_growth_negative test #326 — fixes the broken test PR feat(contract): promote EWA-Sandwich Σ-propagation kernel to lance-graph-contract (B1) #322 shipped (the regression this gate would have caught).
• PR style(shader-driver): drop double-space alignment in bindspace.rs comments #327 — fixes rustfmt drift PR feat(cognitive-shader-driver): add Σ-codebook-index column to FingerprintColumns (B2) #323 introduced.