Add AV1150: Avoid local functions

_rules/1150.md

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+---
+rule_id: 1150
+rule_category: member-design
+title: Avoid local functions
+severity: 3
+---
+Local functions (methods defined inside another method) can be useful in rare cases, but they often obscure a method's structure and make unit testing harder. Their usage often indicates a lack of proper decomposition.
+
+Local functions can be a good fit for:
+- Trivial private recursion.
+- Iterator implementations (validate inputs upfront in the containing method, instead of during deferred execution).
+- Extracting to a method would require passing many parameters that are otherwise captured.