regen meter: rely on var for spec regen cycle

[Macweese]

This PR migrates the tracking of the special attack regeneration cycle to use vars instead. Additionally, the regeneration cycle may desync if e.g. the plugin is enabled mid cycle; thus a check is added to ensure the regeneration cycle remains accurate.

Keeping the spec cycle value on initialization to a default 50 ticks was deliberate with this change because I am not sure which event runs first, as to not risk division by zero here.