refactor: rename id_generator to snowflake

src/snowflake/snowflake.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+#include <stdint.h>
+
+struct snowflake_options
+{
+    uint8_t snowflake_base;
+    uint8_t snowflake_offset;
+};
+
+// return  0: success
+// return -1: failed
+int snowflake_id_init(const struct snowflake_options *opts);
+uint64_t snowflake_id_generate(uint64_t now_sec);
+
+#ifdef __cplusplus
+}
+#endif