Streaming errors for encoders

[teh-cmc]

This is a simple change to make our encoding methods take iterators of results instead of iterators of unwrapped values.

In most (all?) real-world scenarios, you will have to deal with errors as you serialize LogMsgs.
The previous design forced you to collect all that data in order to first check for errors, and only then start encoding. Now you can just stream as needed.
In the rare case where nothing can fail, you're just one .map(Ok) away anyway.

As a side-effect, rerun rrd merge|compact now streams their output.

• DNM: requires Improved CLI: stdin streaming support #7092
• Related to Viewer's save-to-file feature should stream to the IO thread #6984

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
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  • Using examples from latest main build: rerun.io/viewer
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• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

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[jleibs]

Nice!