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 serde_ipld_dagcbor. 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
- [ ] Maps with integer keys are decoded without error (ex: hex `a10000` becomes `{"": 0}`)
- [x] Big nums are encoded (ex: `c249010000000000000000`)
- [x] Trying to encode tagged objects (that are not CIDs) will not raise an error
- Ex: `c07819323032352d30352d32365431363a31383a31372d30343a3030` ([view](https://cbor.nemo157.com/#type=hex&value=c07819323032352d30352d32365431363a31383a31372d30343a3030))
- I am decoding this with ciborium and holding it in a [Value](https://docs.rs/ciborium/latest/ciborium/value/enum.Value.html)
- Encoding output from serde_ipld_dagcbor: `a16a4040544147474544404082007819323032352d30352d32365431363a31383a31372d30343a3030` ([view](https://cbor.nemo157.com/#type=hex&value=a16a4040544147474544404082007819323032352d30352d32365431363a31383a31372d30343a3030))
- Let me know if this bug is not relevant as I'm not that familiar with Rust

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