refactor(ir): 将IR节点重构为值引用并添加字符串字面量支持

- 将scc_ir_node_ref_t重命名为scc_ir_value_ref_t，并更新所有相关API
- 修改IR定义中的节点标签枚举为值标签枚举(scc_ir_node_tag_t -> scc_ir_value_tag_t)
- 更新AST到IR转换器中所有节点引用的类型声明
- 添加对内置类型(VOID, CHAR, INT等)的完整映射实现
- 实现字符串字面量的常量数组创建功能
- 更新项目名称从"Simple Modual C Compiler"为"Simple C Compiler"
- 在Doxyfile中排除external目录的文档生成
- 移除未使用的strpool字段并重命名decl到IR的映射表

BREAKING CHANGE: IR节点引用类型已更改，所有使用scc_ir_node_ref_t的地方需
替换为scc_ir_value_ref_t。

libs/ir/src/scc_ir.c

@@ -55,8 +55,8 @@ void scc_ir_func_init(scc_ir_func_t *in, const char *name) {
     scc_vec_init(in->params);
 }
 
-void scc_ir_node_init(scc_ir_node_t *in, const char *name,
-                      scc_ir_node_tag_t tag) {
+void scc_ir_node_init(scc_ir_value_t *in, const char *name,
+                      scc_ir_value_tag_t tag) {
     Assert(in != null);
     in->name = name;
     in->tag = tag;
@@ -64,44 +64,44 @@ void scc_ir_node_init(scc_ir_node_t *in, const char *name,
     in->type = 0;
 
     switch (tag) {
-    case SCC_IR_NODE_NULL:
+    case SCC_IR_VALUE_TAG_NULL:
         break;
-    case SCC_IR_NODE_CONST_INT:
+    case SCC_IR_VALUE_TAG_CONST_INT:
         // TODO
         in->data.const_int.int64 = 0;
         break;
-    case SCC_IR_NODE_ALLOC:
+    case SCC_IR_VALUE_TAG_ALLOC:
         // TODO();
         break;
-    case SCC_IR_NODE_LOAD:
+    case SCC_IR_VALUE_TAG_LOAD:
         in->data.load.target = 0;
         break;
-    case SCC_IR_NODE_STORE:
+    case SCC_IR_VALUE_TAG_STORE:
         in->data.store.target = 0;
         in->data.store.value = 0;
         break;
-    case SCC_IR_NODE_GET_PTR:
+    case SCC_IR_VALUE_TAG_GET_PTR:
         in->data.get_ptr.src_addr = 0;
         in->data.get_ptr.index = 0;
         break;
-    case SCC_IR_NODE_OP:
+    case SCC_IR_VALUE_TAG_OP:
         in->data.op.op = SCC_IR_OP_EMPTY;
         in->data.op.lhs = 0;
         in->data.op.rhs = 0;
         break;
-    case SCC_IR_NODE_BRANCH:
+    case SCC_IR_VALUE_TAG_BRANCH:
         in->data.branch.cond = 0;
         in->data.branch.true_bblock = 0;
         in->data.branch.false_bblock = 0;
         break;
-    case SCC_IR_NODE_JUMP:
+    case SCC_IR_VALUE_TAG_JUMP:
         in->data.jump.target_bblock = 0;
         break;
-    case SCC_IR_NODE_CALL:
+    case SCC_IR_VALUE_TAG_CALL:
         scc_vec_init(in->data.call.args);
         in->data.call.callee = 0;
         break;
-    case SCC_IR_NODE_RET:
+    case SCC_IR_VALUE_TAG_RET:
         in->data.ret.ret_val = 0;
         break;
     default: