Synchronize customization, gadgets, items, and shops

[Patrick-van-Halm]

Summary

This PR expands multiplayer world synchronization to cover vehicle customization, gadgets, soldering, item reconciliation, and shop purchases. It also hardens item ownership and late-join restoration so clients converge on the same world state without relying on every relevant scene or object being loaded at the same time.

What changed

Customization and gadgets

• Synchronizes gadget placement and removal, drilling holes, mounting, wiring, snapping, spool changes, duct-tape replacement, and soldering.
• Tracks mutable gadget state such as channels, modes, switches, text, timers, mounting points, and soldering progress.
• Captures a complete customization snapshot for joining clients and applies it in dependency order.
• Defers placements, relationships, and hole state until their items and customization targets are ready.
• Prevents remotely applied actions from being echoed back onto the network.

Items and late-join reconciliation

• Adds explicit client/server item reconciliation packets and shared reconciliation rules.
• Restores referenced items before applying customization relationships that depend on them.
• Synchronizes extensible tracked values through a central serializer instead of adding gadget-specific fields to the base item protocol.
• Improves item creation, deletion, ownership, storage, and dropped-item handling when objects load in a different order on each peer.
• Reconciles player and train state after late joins and scene transitions.

Shops and ownership

• Coordinates purchases through the host while preserving the initiating player's ownership of purchased items.
• Synchronizes approved baskets and global shop stock across peers.
• Scales stock allowances for multiplayer without overwriting zero-value lockouts or unrelated runtime overrides.
• Recounts existing shop items when initializing synchronized stock.
• Fixes lost-and-found and storage flows that could otherwise assign ownership to the wrong player.
• Integrates shop registers with the existing networked cash-register lifecycle.

Architecture

• CustomizationStateManager owns capture, deferred restoration, and application of customization actions.
• GadgetTrackedValueRegistry maps game gadget types onto the generic tracked-value item protocol.
• NetworkedItemManager remains responsible for item identity, lifecycle, ownership, and reconciliation.
• ShopPurchaseCoordinator isolates shop inventory and purchase semantics from packet transport and Harmony patches.
• Harmony patches observe game actions at their source, while synchronization scopes prevent feedback loops during remote application.
• The host relays shared world changes and coordinates purchases; ordinary customization interactions remain client-authoritative because the host may not have the initiating player's area loaded.