SequenceArray cannot cast to a narrower type

[danking]

Describe the bug

The sequence array [30, 20, 10, 0] should be castable to u8, but it is not because its multiplier is -10.

Sequence Array should use one PType for calculation and a different PType for the return value.

See also: https://github.com/vortex-data/vortex/pull/5101

To Reproduce

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Expected behavior

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Additional context

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