Input clock reference: bump maximum gap to 60s

Some APE files can have a single packet duration of up to 30s
Is there even a hard limit in this format, or can packets be longer?

Previous gap limit was an arbitrary 22s, written in a way reminiscent of
the MPEG 90kHz clock, which does not make sense anymore since reference clock
in all our demuxers use our own 1MHz clock.

Also explicitely use CLOCK_FREQ