Add comprehensive world package tests and serialization

[fabricekabongo]

Summary

• update world serialization to encode namespaced locations into gob-friendly DTOs
• add extensive world package tests covering validation, panics, and quadtree behaviors to reach full coverage

Testing

• go test ./...
• go test ./world -cover

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Codex Task

[deepsource-io]

Here's the code health analysis summary for commits 550b40e..974f781. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Docker	✅ Success		View Check ↗
Secrets	✅ Success		View Check ↗
Test coverage	✅ Success		View Check ↗
Go	✅ Success		View Check ↗

Code Coverage Report

Metric	Aggregate	Go
Composite Coverage	62.2% (up 6.6% from main)	62.2% (up 6.6% from main)
Line Coverage	62.2% (up 6.6% from main)	62.2% (up 6.6% from main)
New Composite Coverage	100%	100%
New Line Coverage	100%	100%

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