fix(emit-format): handle chained method call in formatCallExpr

[notJoon]

Summary

• Fix panic when processing chained method calls (e.g., ctx.Caller().String()) in emit format rule
• Add formatEmitExpr helper to safely handle various ast.Expr types

Problem

The formatCallExpr function assumed SelectorExpr.X is always *ast.Ident, causing a panic when encountering chained method calls like obj.Method().AnotherMethod() where X is *ast.CallExpr.

Changes

• Replace unsafe type assertion with formatEmitExpr helper that handles *ast.Ident, *ast.CallExpr, and *ast.SelectorExpr
• Add test case for chained method calls