basic/calendarspec: set a limit on length of calendarspec component chains

basic/calendarspec: set a limit on length of calendarspec component chains

We probably should allow very deep calls of our recursive functions. Let's add
a limit to avoid resource exhaustion. 240 is 10 per hour (if somebody is using
this for time based triggers...), so it should be more than enough for most use
cases, and is conveniently below the 250 stack limit in msan.

oss-fuzz #6917.