Detect enclosing function for C#

[xaldama]

Summary

• Implements enclosing function detection for C# (FQN format: Namespace.ClassName.MethodName(ParamType1, ParamType2))
• Handles methods, constructors, and local functions
• Supports nested namespaces and the C# 10 file-scoped namespace Foo.Bar; syntax

Test plan

• Unit tests in csharp/methods.rs cover methods, constructors, local functions, namespaces, parameters, and attribute decorators

[datadog-datadog-prod-us1]

🎯 Code Coverage (details)
• Patch Coverage: 91.94%
• Overall Coverage: 85.17% (+0.05%)

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