perf: demote audited movement and menu packets to narrower execution lanes

[carabistouflette]

Type of change

• Block implementation
• Item implementation
• Command implementation
• Entity implementation
• Bug fix
• New feature
• Breaking change
• Refactor / code cleanup
• Performance improvement

Description

Concurrency audit of the scheduled packet lanes (see per-handler notes in ScheduledPlayPacketKind::execution):

• MovePlayer / MoveVehicle → PlayerLocal (was Serialized). The handlers mutate only per-player movement and teleport state behind SyncMutex and route through chunk-map ticket APIs with fine-grained internal locks; collision lookups are read-only. This takes the hottest packet path off the global serialized lane.
• ContainerButtonClick / ContainerSlotStateChanged → Serialized (was Exclusive). Menu transactions serialize on the menu lock exactly like ContainerClick, so the full global barrier was unnecessarily wide.
• Attack, Interact, CustomPayload, PlayerAction::ReleaseUseItem remain Exclusive: combat spans independently locked source and target state; custom payloads have no constrained resource contract.

The ScheduledPacketExecution doc comment documents the per-lane safety invariants.

How this was tested

• Classification tests updated: packet_execution_classification_separates_local_and_serialized_work now asserts MovePlayer = PlayerLocal; new menu_transactions_share_the_serialized_lane asserts Click/ButtonClick/SlotStateChanged = Serialized; cross_player_handlers_remain_global_barriers (renamed) asserts Attack/Interact/ReleaseUseItem = Exclusive.
• cargo test -p steel-core --lib (2423 tests) pass; cargo clippy -r --all-targets clean.

Screenshots / logs

N/A.

Checklist

• Code builds w/o errors or warnings
• Self-reviewed the diff
• Docs updated (if applicable) — N/A
• No leftover debug code / comments

Additional notes

• Contingency from the audit plan: if profiling surfaces unexpected contention on chunk-map tickets under MovePlayer concurrency, MovePlayer can fall back to Serialized while keeping the menu demotions.
• Env: Linux, Rust nightly, Minecraft protocol 776 (0.15.2+mc26.2).