feat(audit): add persistent AuditLog storage foundation

[jscott3201]

Summary

• move dependency-neutral Audit notification/query/record models into bacnet-types and reusable constructed codecs into bacnet-encoding, while preserving the existing bacnet_services::audit paths and wire behavior
• add an object-owned AuditLogPersistence port plus a concrete two-slot, versioned, checksummed file backend
• persist retained typed records, sequence identities, capacity, Enable, and Total_Record_Count as one coherent snapshot
• commit and synchronize prospective state before replacing observable memory; fall back only from recoverable corruption and fail closed on I/O, incompatible schema/identity, or divergent same-generation slots
• enforce BACnet Audit Log count/wrap/status rules, keep Record_Count read-only, and require explicit Rust/Python per-object storage configuration

Standard and scope

This is the persistence-first foundation required by ANSI/ASHRAE 135-2020 §3.1 and §12.64. It establishes restart-safe object state and the dependency boundary needed by the later query slice.

It deliberately does not add AuditLogQuery dispatch, notification ingestion, authorization, replay, automatic migration/repair, multi-process locking, or public conformance claims. Portable power-loss behavior is not claimed beyond successful slot-file synchronization.

Compatibility

• AuditLogObject::new now requires an injected persistence backend.
• Python add_audit_log now requires an explicit storage_path.
• the legacy description-only Audit record is replaced by the typed BACnet Audit record model.

Validation

Final-head checks:

• cargo test -p bacnet-objects audit --locked — 14 passed
• cargo fmt --all -- --check
• cargo check -p bacnet-objects --tests --target x86_64-pc-windows-gnu --locked
• git diff --check

Implementation-pass checks (the subsequent bounded repair touched only Audit object/persistence code and reran its focused suite):

• cargo test -p bacnet-types audit --locked
• cargo test -p bacnet-encoding audit --locked
• cargo test -p bacnet-services audit --locked
• cargo test -p bacnet-server wpm_rollback_contract --locked
• cargo check -p rusty-bacnet --tests --locked
• cargo clippy --workspace --exclude rusty-bacnet --all-targets --locked
• cargo test --workspace --exclude rusty-bacnet --locked
• conformance-doc, file-size, and no-secret checks

Hosted Windows runtime qualification remains required because this slice adds a concrete filesystem backend.

Refs #345

[jscott3201]

Final gate record for head 5f9ff36: holistic and dataflow immutable reviews PASS; lean dev CI PASS; supplemental draft PR #459 PASS on Windows, macOS, Ubuntu, MSRV, Clippy, Rustfmt, Cargo Deny, file-size, and no-secret checks. Supplemental Cargo Audit found pre-existing RUSTSEC-2026-0258 in unchanged h2 0.4.15; owner authorized merge of this dependency-neutral PR with an immediate dedicated h2 0.4.16 follow-up. PR #459 was closed without merge.