test: add regression tests for issue #1370

Add three regression test cases for cross-package interface private method calls:

1. _cmptest/issue1370_gotypes/ - Tests go/types.Object interface with Scope.Insert()
   which calls the private setParent() method

2. _cmptest/issue1370_goast/ - Tests go/ast.Expr interface conversion with ast.Ident
   which has a private exprNode() method

3. _cmptest/issue1370_geometry/ - Tests custom geometry.Shape interface with private
   methods (validate, setID) across package boundaries

These tests verify the fix in ssa/abitype.go correctly sets the interface metadata's
PkgPath to the interface definition package instead of the compilation package,
preventing segmentation faults when calling private methods.

Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <51194195+luoliwoshang@users.noreply.github.com>

_cmptest/issue1370_geometry/geometry.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/goplus/llgo/_cmptest/issue1370_geometry/geometry"
+)
+
+func main() {
+	rect := geometry.NewRectangle(5.0, 3.0)
+
+	err := geometry.RegisterShape(rect, 42)
+	if err != nil {
+		println("FAIL: RegisterShape returned error")
+		return
+	}
+
+	if rect.GetID() != 42 {
+		println("FAIL: ID not set correctly")
+		return
+	}
+
+	area := rect.Area()
+	fmt.Printf("Area: %.1f\n", area)
+
+	if area != 15.0 {
+		println("FAIL: Area calculation incorrect")
+		return
+	}
+
+	println("SUCCESS: Custom interface with private methods works correctly")
+}

_cmptest/issue1370_geometry/geometry/geometry.go

@@ -0,0 +1,26 @@
+package geometry
+
+type Shape interface {
+	Area() float64
+	validate() bool
+	setID(int)
+}
+
+type Rectangle struct {
+	Width, Height float64
+	id            int
+}
+
+func (r *Rectangle) Area() float64  { return r.Width * r.Height }
+func (r *Rectangle) validate() bool { return r.Width > 0 && r.Height > 0 }
+func (r *Rectangle) setID(id int)   { r.id = id }
+func (r *Rectangle) GetID() int     { return r.id }
+
+func NewRectangle(width, height float64) *Rectangle {
+	return &Rectangle{Width: width, Height: height}
+}
+
+func RegisterShape(s Shape, id int) error {
+	s.setID(id)
+	return nil
+}

_cmptest/issue1370_goast/goast.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+)
+
+func main() {
+	ident := &ast.Ident{
+		NamePos: token.Pos(42),
+		Name:    "foo",
+	}
+
+	var expr ast.Expr = ident
+	pos := expr.Pos()
+
+	fmt.Printf("Position: %d\n", pos)
+	if pos != 42 {
+		println("FAIL: Position mismatch")
+		return
+	}
+
+	println("SUCCESS: ast.Expr interface method calls work correctly")
+}

_cmptest/issue1370_gotypes/gotypes.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"go/types"
+)
+
+func main() {
+	scope := types.NewScope(nil, 0, 0, "test")
+	obj := types.NewVar(0, nil, "x", types.Typ[types.Int])
+
+	scope.Insert(obj)
+
+	retrieved := scope.Lookup("x")
+	if retrieved == nil {
+		println("FAIL: Lookup returned nil")
+		return
+	}
+	if retrieved.Name() != "x" {
+		println("FAIL: Name mismatch")
+		return
+	}
+
+	println("SUCCESS: Scope.Insert and Lookup work correctly")
+}