Fix XmlDeserializer when XML uses same tag in nested elements

[alexeyzimarev]

User description

Description

Replaces #2336

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Auto-created Ticket

#2340

PR Type

Bug fix

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Description

• Fix XmlDeserializer to use Elements() instead of Descendants() for nested XML elements

• Prevent deeply nested elements from being incorrectly included in parent lists

• Handle duplicate element names by preferring shallowest RootElement match

• Remove null values from namespace filtering and fix null-forgiving operators

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Diagram Walkthrough

flowchart LR
  A["XmlDeserializer"] -->|"RootElement selection"| B["Prefer shallowest match<br/>Element() then DescendantsAndSelf()"]
  A -->|"HandleListDerivative"| C["Use Elements() on containers<br/>Descendants() as fallback"]
  A -->|"RemoveNamespace"| D["Filter null attributes"]
  A -->|"Type conversion"| E["Remove null-forgiving operators"]

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File Walkthrough

	Relevant files
Bug fix	XmlDeserializer.cs Refactor nested element handling with Elements() strategy src/RestSharp.Serializers.Xml/XmlDeserializer.cs Modified RootElement selection to prefer shallowest match using Element() first, then DescendantsAndSelf() ordered by ancestor count Refactored HandleListDerivative to detect container elements and use Elements() for direct children only, preventing nested list flattening Extracted element name variation logic into new TryFindElementsByNameVariations() method supporting both direct children and descendants modes Added IsValidXmlElementName() helper to filter out generic type names containing backticks Fixed RemoveNamespace() to filter null attribute values Removed unnecessary null-forgiving operators (!) from ToString() calls +117/-29
Tests	NestedElementTestClasses.cs Add test classes for nested element scenarios                        test/RestSharp.Tests.Serializers.Xml/SampleClasses/NestedElementTestClasses.cs Added Item class with recursive SubItems list for testing nested structures Added ItemContainer class to hold list of Items Added ItemWithGroup and ItemGroup classes for testing grouped nested items Added ItemsResponse class for testing complex nested scenarios +25/-0    XmlDeserializerTests.cs Add comprehensive tests for nested element fixes                  test/RestSharp.Tests.Serializers.Xml/XmlDeserializerTests.cs Added test for Bug Add support for downloading gzip'd content #1: nested lists should not include deeply nested items Added test for Bug Add support for file downloading #2: RootElement with duplicate nested names should not throw Added test for Bug Add support for file downloading #2: RootElement should prefer shallowest match Added test for Bug Add support for file downloading #2: RootElement should try direct child first Added tests for container-based list deserialization using direct children only Added test for deeply nested items with multiple levels of nesting +165/-1

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PR Compliance Guide 🔍

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🟢	No security concerns identified No security vulnerabilities detected by AI analysis. Human verification advised for critical code.
Ticket Compliance
⚪	🎫 No ticket provided Create ticket/issue
Codebase Duplication Compliance
🟢	No codebase code duplication found New Components Detected (Top 5): - Deserialize_Nested_List_Should_Not_Include_Deeply_Nested_Items - Deserialize_RootElement_Should_Not_Throw_On_Duplicate_Nested_Names - Deserialize_RootElement_Should_Prefer_Shallowest_Match - Deserialize_RootElement_Should_Try_Direct_Child_First - Deserialize_List_With_Container_Should_Use_Direct_Children_Only
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