Implement beast of burden storage for summoning familiars

[maatheusgois-dd]

Summary

• Implements Store / Take BoB for beast-of-burden familiars (e.g. pack yak): withdraw/store items via beast_of_burden (671) and summoning_side (722) interfaces.
• Registers the beast_of_burden inventory (id 530, 6×5) and wires examine handlers.
• On dismiss, drops stored BoB items to the ground and closes the BoB interface.
• Adds familiar_leash timer and improves Follow teleport so familiars auto-call when they drift >15 tiles (skipped while in combat).
• Removes the "Not currently implemented" Take BoB stub.

Test plan

• BeastOfBurdenStoreTest — store/withdraw round-trip
• BeastOfBurdenZeroSizeTest — empty undersized inv recreated correctly
• BeastOfBurdenDisplayTest — interface sync after store
• PackYakDefinitionTest — pack yak has BoB capacity from NPC def
• Manual: summon pack yak → Interact → Store items → withdraw → Take BoB → dismiss (items drop)
• Manual: walk familiar >15 tiles away → familiar teleports back

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