[keelerm84]

FlagBuilderV2#value_for_all set a single variation but kept the off
variation, which is 1 for a new flag. That index is out of range, so the
flag failed to evaluate when targeting was off. The method now also sets
the off variation to the single variation, so the flag returns the value
whether targeting is on or off, as its documentation says.

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Note

Overview
Fixes TestDataV2 FlagBuilderV2#value_for_all so flags with a single custom variation evaluate correctly when targeting is off.

The method already collapsed the flag to one variation and set fallthrough to index 0, but it left off variation at the default boolean flag index (1). With only one variation, that index is invalid and evaluation could fail with targeting off. The builder now also calls off_variation(0), matching the documented behavior of returning the same value whether targeting is on or off.

Adds a spec that built flags expose offVariation 0 for both targeting on and off.

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