feat(server): receive unconfirmed audit notifications

[jscott3201]

Summary

• receive direct and routed UnconfirmedAuditNotification requests through a distinct fail-closed authorization context
• preserve silent no-response behavior, bounded admission, and atomic durable Audit Log storage
• advertise executed service bit 46 and update qualified Rust/conformance documentation

Standards and scope

Grounded against Standard 135-2020 §13.21, §19.6, and Annex K §K.8. This PR advances receipt only. It does not add producers, forwarding, durable idempotency, sustained rate limiting, multi-log routing, or a full AR-L-A/BIBB claim.

Refs #345

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --exclude rusty-bacnet --all-targets --locked
• cargo test --workspace --exclude rusty-bacnet --locked
• cargo test -p bacnet-server sc_builder_exposes_the_same_explicit_receiver_policy --features sc-tls --locked
• cargo check -p rusty-bacnet --tests --locked
• python3 scripts/generate-conformance-docs.py --check
• bash .github/scripts/check-file-size.sh
• bash .github/scripts/check-no-secrets.sh
• git diff --check