Defensively test against mistakes found in the advisory db

[CosmicHorrorDev]

I figured it would be worthwhile to start digging through issues reported in the advisory-db. So far it hasn't found anything interesting, but this includes areas that could have issues from future optimizations (primarily avoiding extra bounds/capacity checking)

This is just the first set since there's more I would like to add (namely around panicking in either clone() or drop(), but that seems fine so far). Common sources of issues seem to be

• Wrong Send or Sync bounds: already fixed
• Forgetting to bounds check, or off by one error when bounds checking: already seems decently tested, but could be worth some property testing
• Panicking in unexpected places: everything seems to update the bounds correctly to avoid dropping things multiple times, but could use some more testing since it's something that could get some error-prone performance improvements in the future
• Using incorrect alignment: seems fine to me at a glance, and has some existing tests
• Multiple mutable references to the same data: seems to correctly check uniqueness before allowing for mutation, although some more debug_assert!s wouldn't hurt
• Use after free: Only issue I found was that extremely degenerate clone() issue. All the lifetimes seem right, so far
• Making assumptions about #[repr(Rust)] layout: EcoVec seems appropriately #[repr(C)] and running with RUSTFLAGS="-Zrandomize-layout" didn't find any issues

Still have more auditing to do, but so far things seem very solid :+1:

[codecov[bot]]

Codecov Report

Base: 86.68% // Head: 86.68% // No change to project coverage :thumbsup:

Coverage data is based on head (d8c31a9) compared to base (ebcbaa1). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #19 +/- ## ======================================= Coverage 86.68% 86.68% ======================================= Files 5 5 Lines 1359 1359 ======================================= Hits 1178 1178 Misses 181 181 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=typst)

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[laurmaedje]

Nice!