[Elm] Fix List of type missing required import(s)

[Qluxzz]

Currently, if you have the type List Uuid, the needed import from Uuid won't be included. This is the same for List Posix which doesn't include the needed import from Api.Time.

Fixed so function recursively checks if the list's item type is UUID or Posix, and then sets flags (includeUuid/includeTime) accordingly.

Added test cases to validate changes.

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  @eriktim

[wing328]

Thanks for the PR and the tests. Let's give it a try.