release-24.2: stats, encoding: improve UUID-decoding error

[blathers-crl]

Backport 1/1 commits from #136015 on behalf of @michae2.

/cc @cockroachdb/release

---

Add a length check to DecodeUUIDValue and a more informative error wrapping to DecodeUpperBound, which will hopefully help us track down the cause of #128876.

The wrapped error message looks like:

decoding histogram version 3 type uuid value ‹666f6f›: invalid uuid length of 2

Informs: #128876

Epic: None

Release note: None

---

Release justification: low-risk debugging for error.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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  issues or test-only changes.
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[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[yuzefovich]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @michae2, @mw5h, and @rytaft)