Client-originated unknown unicast now has its own relay-side token bucket.
When a client sends to an unlearned unicast MAC, the relay consumes from that
bucket before flooding the frame to the room.
Known unicast to a registered client bypasses this limit, and broadcast or
multicast traffic continues to use its separate bucket. Keeping the buckets in
room state matches the existing forwarding-policy ownership and lets unit tests
drive explicit instants.
This is the second rate-limit slice from PLAN.md. A total bandwidth cap remains
future work.
Test Plan:
- cargo fmt --check
- cargo test -p lanparty-relay
- cargo clippy -p lanparty-relay --all-targets -- -D warnings
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings
- git diff --check
Refs: PLAN.md
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