Seed all pecos-neo test simulators and enforce determinism with a source scan

[ciaranra]

Follow-up to #454, implementing the prevention decided after the test_multiple_shots flake: pecos-neo test code is now deterministic by construction, and a scan enforces it.

• 230 simulator constructions in test code migrated to seeded constructors (218 SparseStab, 10 StateVec, 2 StateVecEngine), across tests/ and every #[cfg(test)] module. Runtime code and doc examples are untouched; no new APIs were needed.
• New tests/determinism_discipline.rs: scans the crate's own sources (tests/ entirely, plus #[cfg(test)] regions in src/, including external mod tests; files) and fails on any entropy-seeded simulator constructor, with an empty allowlist and a message naming the file, line, and seeded alternative. Non-vacuity assertions prove the scan reads real code.
• Mutation-verified twice (implementation and an independent re-check): reintroducing SparseStab::new( in either a tests/ file or a #[cfg(test)] module fails the scan naming the site.
• Full crate suite green: 957 unit tests, all integration binaries, 206 doctests; clippy and fmt clean.

Context recorded in #332: the canonical RNG platform should eventually make whole-run determinism single-knob; this PR makes the test suite deterministic today without preempting that design.