feat(demo): add result verification to go/token and go/types demos

Added comprehensive result verification and assertions to ensure correctness:

go/token demo:
- Verify Pos values and IsValid() results
- Check token string representations
- Validate keyword detection (IsKeyword())
- Assert operator precedence relationships
- Verify file and position operations

go/types demo:
- Validate basic type kinds
- Check object names and types (Var, Const, Func, TypeName)
- Verify package path and name
- Assert interface method counts and names
- Check struct field counts, names, and types
- Validate signature params and results
- Verify tuple, array, slice, pointer, map, and chan properties

All demos now fail fast with panic() if results don't match expected values,
providing better test coverage than just printing output.

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

_demo/go/gotoken/main.go

@@ -22,10 +22,26 @@ func testPos() {
 	pos1 := token.Pos(100)
 	pos2 := token.Pos(200)
 	
+	if pos1 != 100 {
+		panic(fmt.Sprintf("Expected pos1 to be 100, got %d", pos1))
+	}
+	if pos2 != 200 {
+		panic(fmt.Sprintf("Expected pos2 to be 200, got %d", pos2))
+	}
 	fmt.Printf("Pos1: %d, Pos2: %d\n", pos1, pos2)
+	
+	if !pos1.IsValid() {
+		panic("Expected pos1.IsValid() to be true")
+	}
 	fmt.Printf("Pos1.IsValid(): %v\n", pos1.IsValid())
 	
 	noPos := token.NoPos
+	if noPos != 0 {
+		panic(fmt.Sprintf("Expected NoPos to be 0, got %d", noPos))
+	}
+	if noPos.IsValid() {
+		panic("Expected NoPos.IsValid() to be false")
+	}
 	fmt.Printf("NoPos: %d, IsValid: %v\n", noPos, noPos.IsValid())
 	
 	fmt.Println("SUCCESS: Pos operations work correctly\n")
@@ -34,6 +50,23 @@ func testPos() {
 func testToken() {
 	fmt.Println("\n=== Test Token Types ===")
 	
+	expectedStrings := map[token.Token]string{
+		token.ADD:    "+",
+		token.SUB:    "-",
+		token.MUL:    "*",
+		token.QUO:    "/",
+		token.LPAREN: "(",
+		token.RPAREN: ")",
+		token.EQL:    "==",
+		token.NEQ:    "!=",
+	}
+	
+	for tok, expected := range expectedStrings {
+		if tok.String() != expected {
+			panic(fmt.Sprintf("Expected %v.String() to be %q, got %q", tok, expected, tok.String()))
+		}
+	}
+	
 	tokens := []token.Token{
 		token.ILLEGAL,
 		token.EOF,
@@ -132,15 +165,38 @@ func testTokenKeywords() {
 	}
 	
 	for _, kw := range keywords {
+		if !kw.IsKeyword() {
+			panic(fmt.Sprintf("Expected %s to be a keyword", kw))
+		}
 		fmt.Printf("Keyword: %s, IsKeyword: %v\n", kw, kw.IsKeyword())
 	}
 	
+	if token.ADD.IsKeyword() {
+		panic("Expected ADD operator to not be a keyword")
+	}
+	if token.IDENT.IsKeyword() {
+		panic("Expected IDENT token to not be a keyword")
+	}
+	
 	fmt.Println("SUCCESS: Keyword checks work correctly\n")
 }
 
 func testTokenPrecedence() {
 	fmt.Println("\n=== Test Token Precedence ===")
 	
+	if token.MUL.Precedence() <= token.ADD.Precedence() {
+		panic("Expected MUL to have higher precedence than ADD")
+	}
+	if token.LAND.Precedence() <= token.LOR.Precedence() {
+		panic("Expected LAND to have higher precedence than LOR")
+	}
+	if token.MUL.Precedence() != token.QUO.Precedence() {
+		panic("Expected MUL and QUO to have same precedence")
+	}
+	if token.ADD.Precedence() != token.SUB.Precedence() {
+		panic("Expected ADD and SUB to have same precedence")
+	}
+	
 	operators := []token.Token{
 		token.ADD,
 		token.SUB,
@@ -190,10 +246,21 @@ func testFile() {
 	fset := token.NewFileSet()
 	file := fset.AddFile("test.go", -1, 1000)
 	
+	if file.Name() != "test.go" {
+		panic(fmt.Sprintf("Expected file name to be 'test.go', got %q", file.Name()))
+	}
+	if file.Size() != 1000 {
+		panic(fmt.Sprintf("Expected file size to be 1000, got %d", file.Size()))
+	}
+	
 	file.AddLine(0)
 	file.AddLine(50)
 	file.AddLine(100)
 	
+	if file.LineCount() != 3 {
+		panic(fmt.Sprintf("Expected line count to be 3, got %d", file.LineCount()))
+	}
+	
 	fmt.Printf("File name: %s\n", file.Name())
 	fmt.Printf("File base: %d\n", file.Base())
 	fmt.Printf("File size: %d\n", file.Size())
@@ -203,9 +270,15 @@ func testFile() {
 	fmt.Printf("Pos at offset 50: %d\n", pos)
 	
 	offset := file.Offset(pos)
+	if offset != 50 {
+		panic(fmt.Sprintf("Expected offset to be 50, got %d", offset))
+	}
 	fmt.Printf("Offset of pos: %d\n", offset)
 	
 	line := file.Line(pos)
+	if line != 2 {
+		panic(fmt.Sprintf("Expected line to be 2, got %d", line))
+	}
 	fmt.Printf("Line number at pos: %d\n", line)
 	
 	lineStart := file.LineStart(2)
@@ -227,12 +300,28 @@ func testPosition() {
 		Column:   10,
 	}
 	
+	if !pos.IsValid() {
+		panic("Expected valid position to be valid")
+	}
+	if pos.Filename != "test.go" {
+		panic(fmt.Sprintf("Expected filename to be 'test.go', got %q", pos.Filename))
+	}
+	if pos.Line != 5 {
+		panic(fmt.Sprintf("Expected line to be 5, got %d", pos.Line))
+	}
+	if pos.Column != 10 {
+		panic(fmt.Sprintf("Expected column to be 10, got %d", pos.Column))
+	}
+	
 	fmt.Printf("Position: %s\n", pos.String())
 	fmt.Printf("Filename: %s, Line: %d, Column: %d, Offset: %d\n", 
 		pos.Filename, pos.Line, pos.Column, pos.Offset)
 	fmt.Printf("IsValid: %v\n", pos.IsValid())
 	
 	invalidPos := token.Position{}
+	if invalidPos.IsValid() {
+		panic("Expected empty position to be invalid")
+	}
 	fmt.Printf("Invalid position IsValid: %v\n", invalidPos.IsValid())
 	
 	fmt.Println("SUCCESS: Position operations work correctly\n")