Add inits & tails

[JordanMartinez]

Description of the change

• Export tails; make it stack safe
• Implement inits

Note: the inits test currently fails with a "JavaScript heap out of memory" error because we're duplicating a list with 100k elements 999,999 times. Thoughts on how this should proceed?

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Checklist:

• [ ] Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• [ ] Linked any existing issues or proposals that this pull request should close
• [ ] Updated or added relevant documentation
• [ ] Added a test for the contribution (if applicable)