Fix cargo fmt and clippy CI failures in http_preflight

[Copilot]

cargo fmt --check and cargo clippy were both failing in CI, blocking the test_evidence.sh bootstrap stage.

Changes

• Formatting (http_preflight.rs, http_preflight_tests.rs): Applied cargo fmt --all to fix line-length violations in method chains and function call chains.
• Missing struct field (http_preflight.rs): test_state() helper was initializing HttpPreflightState without postflight_etl_path, added after the struct was extended. Fixed by adding postflight_etl_path: PathBuf::from("/dev/null") — writes are discarded, no test semantics change.
• .gitignore: Added crates/*/artifacts/ and proptest-regressions/ to prevent test-generated files from being tracked.

Related references

• AGENTS.md
• TESTING_EVIDENCE.md
• docs/TEST_EVIDENCE.md
• docs/TEST_COVERAGE_MATRIX.md

Change type

• Bug fix
• Feature
• Refactor
• Docs only
• Test-only

Protocol and safety impact

• No protocol logic changes
• Determinism impact reviewed (ordering/hash/canonicalization)
• Panic risk reviewed on request/runtime paths
• Network-facing inputs validated fail-closed
• No secrets/raw payloads added to logs

Testing checklist

• Tests are black-box (public APIs/external behavior)
• Tests do not copy/paste production logic into assertions
• Numeric boundary cases are tested
• Deterministic functions/flows include determinism assertions
• cargo fmt --check passes
• cargo clippy --workspace --all-targets -- -D warnings passes
• cargo test --workspace passes
• No new unsafe code

Evidence

CI run that surfaced both failures: https://github.com/jverdicc/EvidenceOS/actions/runs/22513733985/job/65227872047#step:19:1

Original prompt

Reference: https://github.com/jverdicc/EvidenceOS/actions/runs/22513733985/job/65227872047#step:19:1

Fix this without changing important functionality of the model and system.

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