Updating test.toml for Flatten-Array

[jagdish-15]

Pull Request

@kahgoh, I noticed that the test descriptions were changed after this discussion. I'm unsure whether the changes were only meant to update the test descriptions and the introduction.md file or if they were intended to modify the entire exercise structure—specifically, replacing lists with arrays and requiring a flatten function that accepts an arbitrarily nested array.

Since Java does not support arrays containing mixed data types (like in dynamically typed languages), I assume these updates are just documentation changes. Let me know what you think!

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[kahgoh]

This exercise is a bit problematic since we've used Lists instead of arrays and it looks like the problem specs were updated to just say arrays. I think to allow us to resync this exercise (along with the instructions), I'd suggest addding an instructions.append.md to explain we're using a list instead of an array. It doesn't seem right to just update the test.toml because it changes the test description to use the word "array' instead of "list".

[jagdish-15]

@kahgoh, I've synced the docs for this exercise with problem-specifications and added instructions.append.md as requested. Let me know what the heading for this file should be, as it's required by Lint!