Remove custom NeverOkResult trait and instead use new Rust 1.82 matching

[faern]

In Rust 1.82 we finally get to omit impossible branches in pattern matching: https://blog.rust-lang.org/2024/10/17/Rust-1.82.0.html#omitting-empty-types-in-pattern-matching

This PR utilize that in order to get rid of the custom NeverOkResult trait.

This is not an important change, nor is it a high priority. We might want to wait with merging this until we use Rust 1.82 in the main repo. Just so we don't block ourselves from upgrading to the latest udp-over-tcp in case we need it. I just realized this potential cleanup and wanted to submit a PR while I had it on the top of my mind :)

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This change is 

[dlon]

This is pretty cool. :)

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @faern)