Code Generation Documentation Tracking Issue

- [x] Use examples requiring metadata fixup
- [x] Use examples where fixed header size is not a power of two.
- [x] Use examples with dynamic trailing padding.
- [x] Include pretty-printed assembly.
- [x] Use descriptive benchmark fn name, rather than `codegen_test`
- [ ] Include examples for most of zerocopy's API surface.
- [ ] Ensure codegen tests use pinned nightly tooling.
- See https://github.com/pacak/cargo-show-asm/issues/448
- Optimizations
- [ ] After April 16, use [`core::hint:cold_path`](https://doc.rust-lang.org/beta/std/hint/fn.cold_path.html) on error branches