test: rename some stuff; separate cron part tests

src/cron/vieter_cron_parse.c

@@ -1,4 +1,4 @@
-#include "vieter_cron.h"
+#include "vieter_cron_parse.h"
 #include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>

src/cron/vieter_cron_parse.h

@@ -0,0 +1,11 @@
+#ifndef VIETER_CRON_PARSE
+#define VIETER_CRON_PARSE
+
+#include "vieter_cron.h"
+
+vieter_cron_parse_error vieter_cron_expr_parse_range(uint64_t *out, char *s,
+                                                     uint8_t min, uint8_t max);
+
+vieter_cron_parse_error vieter_cron_expr_parse_part(uint64_t *out, char *s,
+                                                    uint8_t min, uint8_t max);
+#endif