[Ruby] Add `ArrowFormat::ListArray.new(type, values)`

[emecii]

Describe the enhancement requested

Add ArrowFormat::ListArray.new(type, values) so callers can construct a list array from an explicit child type and nested Ruby values, including null lists and null child values.

This is the first nested-array constructor requested in GH-50382 before designing the broader typed-array builder API. It should follow the existing typed constructor style and include focused round-trip coverage.

Component(s)

Ruby

[emecii]

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