Remove stray dbg! from the privacy checker

[dduugg]

Fixes #49.

The bug

src/packs/checker/privacy.rs:64 carried a live dbg!:

dbg!(constant_is_private, constant_is_in_private_namespace);

It fired once per reference checked against a pack's private_constants, in released builds as well as debug, writing two lines to stderr each time and leaking internal file and line numbers into user-facing output.

The fix is deleting the line. src/ now contains no dbg! at all.

Why it survived

Nothing in the suite reached the branch — no fixture configured private_constants. On main, grep -rl private_constants tests/fixtures/ returned nothing, against three hits under src/.

So this adds tests/fixtures/privacy_violations_with_private_constants, exercising all three combinations of the two flags the dbg! was printing:

Reference	Flags	Expected
::Bar	constant_is_private	violation
::Bar::Inner	constant_is_in_private_namespace	violation
::SomeConcern	neither	no violation

The third row is the one worth having. A non-empty private_constants list narrows privacy to that list, so anything in the pack but absent from it stays public — behaviour that previously had no coverage.

test_check_with_private_constants asserts those three outcomes and that stderr is empty, so the dbg! can't return unnoticed.

Verification

I checked the test actually guards the regression rather than merely passing: with the dbg! reinstated it fails on the stderr assertion, reporting all 6 noise lines; with the line removed it passes.

cargo fmt --all -- --check                  clean
cargo clippy --all-targets --all-features   clean
cargo test --test check_test                26 passed

Note on the audit check

The failing audit job is unrelated to this change and pre-dates it. actions-rs/audit-check@v1 cannot compile cargo-audit: the pinned toolchain is rustc 1.92.0 and kstring@2.0.4 now requires 1.96.0. That action has been unmaintained for years (it targets Node 12 and the workflow still pins actions/checkout@v2), and the workflow has never completed successfully on this repo — every earlier run is action_required. This diff touches no Cargo.toml or Cargo.lock, so it cannot affect that job. Being addressed separately.

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