feat: 结构体 struct — 最后一项 P0 功能

- lexer: TOK_STRUCT, TOK_DOT 关键字和运算符
- ast: AST_STRUCT_DECL/STRUCT_INIT/FIELD_ACCESS 3 种新节点
- parser: struct 声明 + .field 访问 + Name{field:val} 初始化
- sema: struct 类型符号表，字段类型解析，初始化字段检查
- codegen: LLVMStructType + extractvalue/insertvalue 字段操作
- 新增集成测试: 12_struct.l, 13_struct_nested.l
- 基于 Codex 分析报告 P0 #4

所有 P0 功能已全部完成。

test/programs/12_struct.l

@@ -0,0 +1,11 @@
+struct Point {
+    x: i64,
+    y: i64,
+}
+
+fn main() -> i64 {
+    let p: Point = Point { x: 10, y: 20 };
+    print_i64(p.x);
+    print_i64(p.y);
+    return 0;
+}

test/programs/13_struct_nested.l

@@ -0,0 +1,19 @@
+struct Point {
+    x: i64,
+    y: i64,
+}
+
+struct Rect {
+    top_left: Point,
+    bot_right: Point,
+}
+
+fn main() -> i64 {
+    let r: Rect = Rect {
+        top_left: Point { x: 0, y: 10 },
+        bot_right: Point { x: 5, y: 0 },
+    };
+    print_i64(r.top_left.x);
+    print_i64(r.bot_right.y);
+    return 0;
+}

test/test_codegen.c

@@ -13,7 +13,7 @@ void test_codegen_simple_function() {
     AstNode* body = ast_make_block(&a, stmts, 1, 1, 1);
     AstNode* fn = ast_make_function(&a, "main", NULL, 0, TYPE_I64, body, 1, 1);
     AstNode* fns[] = { fn };
-    AstNode* prog = ast_make_program(&a, fns, 1, 1, 1);
+    AstNode* prog = ast_make_program(&a, fns, 1, NULL, 0, 1, 1);
 
     const char* err = NULL;
     LLVMModuleRef mod = codegen_module(prog, &a, "test_mod", &err);
@@ -45,7 +45,7 @@ void test_codegen_if_else() {
     AstNode* body = ast_make_block(&a, stmts, 1, 1, 1);
     AstNode* fn = ast_make_function(&a, "main", NULL, 0, TYPE_I64, body, 1, 1);
     AstNode* fns[] = { fn };
-    AstNode* prog = ast_make_program(&a, fns, 1, 1, 1);
+    AstNode* prog = ast_make_program(&a, fns, 1, NULL, 0, 1, 1);
 
     const char* err = NULL;
     LLVMModuleRef mod = codegen_module(prog, &a, "test_mod2", &err);
@@ -74,7 +74,7 @@ void test_codegen_binary_ops() {
     AstNode* body = ast_make_block(&a, stmts, 1, 1, 1);
     AstNode* fn = ast_make_function(&a, "main", NULL, 0, TYPE_I64, body, 1, 1);
     AstNode* fns[] = { fn };
-    AstNode* prog = ast_make_program(&a, fns, 1, 1, 1);
+    AstNode* prog = ast_make_program(&a, fns, 1, NULL, 0, 1, 1);
 
     const char* err = NULL;
     LLVMModuleRef mod = codegen_module(prog, &a, "test_mod3", &err);
@@ -102,7 +102,7 @@ void test_codegen_while_loop() {
     AstNode* fn_body = ast_make_block(&a, stmts, 2, 1, 1);
     AstNode* fn = ast_make_function(&a, "main", NULL, 0, TYPE_I64, fn_body, 1, 1);
     AstNode* fns[] = { fn };
-    AstNode* prog = ast_make_program(&a, fns, 1, 1, 1);
+    AstNode* prog = ast_make_program(&a, fns, 1, NULL, 0, 1, 1);
 
     const char* err = NULL;
     LLVMModuleRef mod = codegen_module(prog, &a, "test_while", &err);