Create tidy-stingrays-think.md

.changeset/tidy-stingrays-think.md

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+---
+"@latticexyz/world": major
+---
+
+Namespaces are not allowed to contain double underscores ("__") anymore, as this sequence of characters is used to [separate the namespace and function selector](https://github.com/latticexyz/mud/pull/2168) in namespaced systems.
+This is to prevent signature clashes of functions in different namespaces.
+
+(Example: If namespaces were allowed to contain this separator string, a function "function" in namespace "namespace__my" would result in the namespaced function selector "namespace__my__function",
+and would clash with a function "my__function" in namespace "namespace".)