Reset countdown for manual casting after each phoneme press

[al0fdf]

Changed the countdown for manual spell casting so that it reset after each phoneme. This means instead of 0.5 seconds under which to cast the whole spell, you have to cast each phoneme within 0.5 seconds of the previous. This should make manual spell casting more approachable.

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[al0fdf]

I am unsure whether ud.SpellCastStart should be re-used in this case. It seems like a misleading name to me, as it's no longer the "start time" of the spell casting, rather the "start time" of the most recent phoneme.

[dennwc]

I manually rebased the PR on dev. Next time please avoid merge commits :)