Integer sequence support for chex.assert_tree_shape{_prefix, _suffix}

[hylkedonker]

Currently, the shape_prefix argument of chex.assert_tree_shape_prefix requires a tuple instead of a integer sequence, as detailed in #274.

This pull request addresses this point, adding support for arbitrary integer sequences, for the following two functions:

• chex.assert_tree_shape_prefix
• chex.assert_tree_shape_suffix

In addition, this pull request adds unit tests to verify this (using lists instead of tuples) for the functions:

• chex.assert_tree_shape_prefix
• chex.assert_tree_shape_suffix
• chex.assert_shape

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[stompchicken]

Thanks for the contribution! I have a suggestion that I think will make some of the tests easier to manage.

[stompchicken]

Thanks a lot for contributing to Chex. I gave approval to merge but also commented on a tiny spelling error.