fix: Go parser fails to extract a package-level variable usage

[angrychow]

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修复：Go parser 不能完整提取包级别的变量依赖关系

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en: We discovered that for an expression like Object.Call(), the parser could only extract the dependency on the method ObjectType.Call() but failed to capture the dependency on the Object instance itself. This behavior is inconsistent with our LSP-based parsers for other languages, which correctly identify this dependency.

zh: 我们发现，对于 Object.Call() 这样的表达式，解析器只能提取出对 ObjectType.Call() 方法的依赖，却未能捕获到对 Object 实例本身的依赖。该行为与我们基于 LSP 的其他语言解析器不一致。

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