provide in-memory world implementation (MapWorldProvider)

While converting some tests from WorldProvidingHeadlessEnvironment to ModuleTestingEnvironment, I discovered that WPHE uses MapWorldProvider, which generates chunks on demand.

There might be a handful of modules providing large-scale features that need to deal with the intricacies of chunk loading, and they should be able to use the default WorldProvider so they don't get a false sense of security. But I think most tests for most modules are only interested a small area, and this on-demand behavior would make things much easier for them. It would eliminate the need for them to use things like forceAndWaitForGeneration.

Inizia confrontando il MapWorldProvider esistente con i percorsi di WorldProvidingHeadlessEnvironment e ModuleTestingEnvironment menzionati nell’issue. Verifica come i test utilizzano attualmente forceAndWaitForGeneration; il lavoro è completato quando la maggior parte dei test dei moduli per aree piccole può usare il provider in memoria con chunk generati on demand, mantenendo il provider predefinito per il comportamento di caricamento dei chunk.