feat(lex_parser): 初始化词法解析器模块

新增词法解析器库 `smcc_lex_parser`，包含基础的词法规则解析功能：
- 支持字符、字符串、数字、标识符的解析
- 支持跳过注释、空白符、行尾等辅助函数
- 提供对应的单元测试用例，覆盖各类合法与非法输入情况

该模块依赖 `libcore`，并被 `smcc_lex` 模块引用以支持更上层的词法分析逻辑。

libs/lex_parser/tests/test_identifier.c

@@ -0,0 +1,55 @@
+// test_identifier.c
+#include <lex_parser.h>
+#include <utest/acutest.h>
+
+cbool check_identifier(const char *str, const char *expect, cstring_t *output) {
+    log_set_level(&__default_logger_root, 0);
+    core_pos_t pos = core_pos_init();
+    core_mem_stream_t mem_stream;
+    core_stream_t *stream =
+        core_mem_stream_init(&mem_stream, str, smcc_strlen(str), false);
+
+    cbool ret = lex_parse_identifier(stream, &pos, output);
+    if (ret && expect) {
+        return strcmp(output->data, expect) == 0;
+    }
+    return ret;
+}
+
+#define CHECK_IDENTIFIER_VALID(str, expect)                                    \
+    do {                                                                       \
+        cstring_t _output = cstring_new();                                     \
+        cbool ret = check_identifier(str, expect, &_output);                   \
+        TEST_CHECK(ret == true);                                               \
+        TEST_CHECK(strcmp(_output.data, expect) == 0);                         \
+        cstring_free(&_output);                                                \
+    } while (0)
+
+#define CHECK_IDENTIFIER_INVALID(str)                                          \
+    do {                                                                       \
+        cstring_t _output = cstring_new();                                     \
+        cbool ret = check_identifier(str, NULL, &_output);                     \
+        TEST_CHECK(ret == false);                                              \
+        cstring_free(&_output);                                                \
+    } while (0)
+
+void test_valid_identifier(void) {
+    TEST_CASE("valid identifiers");
+    CHECK_IDENTIFIER_VALID("variable", "variable");
+    CHECK_IDENTIFIER_VALID("my_var", "my_var");
+    CHECK_IDENTIFIER_VALID("_private", "_private");
+    CHECK_IDENTIFIER_VALID("Var123", "Var123");
+    CHECK_IDENTIFIER_VALID("a", "a");
+}
+
+void test_invalid_identifier(void) {
+    TEST_CASE("invalid identifiers");
+    CHECK_IDENTIFIER_INVALID("");
+    CHECK_IDENTIFIER_INVALID("123var");
+}
+
+TEST_LIST = {
+    {"test_valid_identifier", test_valid_identifier},
+    {"test_invalid_identifier", test_invalid_identifier},
+    {NULL, NULL},
+};