DASL Testing: Tier 1

Hello,

I work on [DASL Testing](https://github.com/hyphacoop/dasl-testing), a project [funded](https://blog.ipfs.tech/2025-05-grants/) by IPFS to test dag-cbor libraries.

I'm filing this issue to report on "Tier 1" bugs we've discovered in libipld. More information is available [here](https://github.com/hyphacoop/dasl-testing/issues/2).

Please feel free to use this issue for tracking bug fixes, asking me questions, or anything else that's helpful.

## Bugs
- [ ] Maps with integer keys can be encoded

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I understand this library is deprecated. I'm just filing this issue to notify maintainers and for completeness, as this library has been added to the DASL Testing suite.

You can view all the tests in more detail on the DASL testing website: https://hyphacoop.github.io/dasl-testing/